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• TypeError: Error #1007: Instantiation attempted on a non-constructor. on port to Flex 4

  - by Josh Handel

  I have been porting an app from Flex 3.4.x to 4.0.. I have successfully ported the app and its libraries to flex 4.0, I've also removed ALL the references to http://www.adobe.com/2006/flex/mx in any of my mxml files... In short I "think" I have moved everything over to the new mx framework (2009).. But I still get the following error (which never happend in 3.4 or 3.5 with this same app) when I try to run my flex app. TypeError: Error #1007: Instantiation attempted on a non-constructor. at mx.preloaders::Preloader/initialize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\preloaders\Preloader.as:253] at mx.managers::SystemManager/http://www.adobe.com/2006/flex/mx/internal::initialize()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:1925] at mx.managers::SystemManager/initHandler()[E:\dev\4.0.0\frameworks\projects\framework\src\mx\managers\SystemManager.as:2419] At this point I am completely stumped.. anyone have any ideas? Thanks

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• Are there ways to improve NHibernate's performance regarding entity instantiation?

  - by denny_ch

  Hi folks, while profiling NHibernate with NHProf I noticed that a lot of time is spend for entity building or at least spend outside the query duration (database roundtrip). The project I'm currently working on prefetches some static data (which goes into the 2nd level cache) at application start. There are about 3000 rows in the result set (and maybe 30 columns) that is queried in 75 ms. The overall duration observed by NHProf is about 13 SECONDS! Is this typical beheviour? I know that NHibernate shouldn't be used for bulk operations, but I didn't thought that entity instantiation would be so expensive. Are there ways to improve performance in such situations or do I have to live with it? Thx, denny_ch

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• Why does Generic class signature requires specifying new() if type T needs instantiation ?

  - by this. __curious_geek

  I'm writing a Generic class as following. public class Foo<T> : where T : Bar, new() { public void MethodInFoo() { T _t = new T(); } } As you can see the object(_t) of type T is instantiated at run-time. To support instantiation of generic type T, language forces me to put new() in the class signature. I'd agree to this if Bar is an abstract class but why does it need to be so if Bar standard non-abstract class with public parameter-less constructor. compiler prompts following message if new() is not found. Cannot create an instance of the variable type 'T' because it does not have the new() constraint

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• Use of private constructor to prevent instantiation of class?

  - by cringe

  Hi guys! Right now I'm thinking about adding a private constructor to a class that only holds some String constants. public class MyStrings { // I want to add this: private MyString() {} public static final String ONE = "something"; public static final String TWO = "another"; ... } Is there any performance or memory overhead if I add a private constructor to this class to prevent someone to instantiate it? Do you think it's necessary at all or that private constructors for this purpose are a waste of time and code clutter?

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• How to signal object instantiation in a Collaboration/Communication Diagram?

  - by devoured elysium

  I'd like to know how to translate the following line of code to a Collaboration Diagram: Food food = new Food("abc", 123); I know that I can call an Food's method using the following notation: MyStaticMethod() ----------------------> -------- | | | Food | | | -------- being that equivalent to Taste taste = Food.MyStaticMethod(); and MyInstanceMethod() ----------------------> --------------- | | | food : Food | | | --------------- is equivalent to food.MyInstanceMethod(); but how do I signal that I want to call a given constructor on Food? Thanks

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• How do I dynamically update an instance array to hold a list of dynamic methods on instantiation?

  - by Will

  I am trying to dynamically define methods based on xml mappings. This works really well. However I want to create an instance variable that is a array of the dynamically defined methods. My code looks something like this def xml_attr_reader(*args) xml_list = "" args.each do |arg| string_val = "def #{arg}; " + " xml_mapping.#{arg}; " + "end; " self.class_eval string_val xml_hash = xml_list + "'#{arg}'," end self.class_eval "@xml_attributes = [] if @xml_attributes.nil?;" + "@xml_attributes = @xml_attributes + [#{xml_list}];" + "puts 'xml_attrs = ' + @xml_attributes.to_s;" + "def xml_attributes;" + " puts 'xml_attrs = ' + @xml_attributes.to_s;" + " @xml_attributes;" + "end" end So everything works except when I call xml_attributes on an instance it return null (and prints out 'xml_attrs = '). While the puts before the definition actually prints out the correct array. (when I instantiate the instance)

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• Can a custom MFC window/dialog be a class template instantiation?

  - by John

  There's a bunch of special macros that MFC uses when creating dialogs, and in my quick tests I'm getting weird errors trying to compile a template dialog class. Is this likely to be a big pain to achieve? Here's what I tried: MyDlg.h template <class W> class CMyDlg : public CDialog { typedef CDialog super; DECLARE_DYNAMIC(CMyDlg <W>) public: CMyDlg (CWnd* pParent); // standard constructor virtual ~CMyDlg (); // Dialog Data enum { IDD = IDD_MYDLG }; protected: virtual void DoDataExchange(CDataExchange* pDX); // DDX/DDV support DECLARE_MESSAGE_MAP() private: W *m_pWidget; //W will always be a CDialog }; IMPLEMENT_DYNAMIC(CMyDlg<W>, super) <------------------- template <class W> CMyDlg<W>::CMyDlg(CWnd* pParent) : super(CMyDlg::IDD, pParent) { m_pWidget = new W(this); } I get a whole bunch of errors but main one appears to be: error C2955: 'CMyDlg' : use of class template requires template argument list I tried using some specialised template versions of macros but it doesn't help much, other errors change but this one remains. Note my code is all in one file, since C++ templates don't like .h/.cpp like normal. I'm assuming someone must have done this in the past, possibly creating custom versions of macros, but I can't find it by searching, since 'template' has other meanings.

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• Class Template Instantiation: any way round this circular reference?

  - by TimYorke34

  I have two classes that I'm using to represent some hardware: A Button and an InputPin class which represent a button that will change the value of an IC's input pin when it's pressed down. A simple example of them is: template <int pinNumber> class InputPin { static bool IsHigh() { return ( (*portAddress) & (1<<pinNumber) ); } }; template <typename InputPin> class Button { static bool IsPressed() { return !InputPin::IsHigh(); } }; This works beautifully and by using class templates, the condition below will compile as tightly as if I'd handwritten it in assembly (a single instruction). Button < InputPin<1> > powerButton; if (powerButton.IsPressed()) ........; However, I am extending it to deal with interrupts and have got a problem with circular references. Compared to the original InputPin, a new InputPinIRQ class has an extra static member function that will be called automatically by the hardware when the pin value changes. I'd like it to be able to notify the Button class of this, so that the Button class can then notify the main application that it has been pressed/released. I am currently doing this with function pointers to callbacks. In order for the callback code to be inlined by the compiler, I need to pass the function pointers as template parameters. So now, both of the new classes have an extra template parameter that is a pointer to a callback function. Unfortunately this gives me a circular reference because to instantiate a ButtonIRQ class I now have to do something like this: ButtonIRQ< InputPinIRQ< A1, ButtonIRQ<....>::OnPinChange, OnButtonChange > pB; where the <...... represents the circular reference. Does anyone know how I can avoid this circular reference? I am new to templates, so might be missing something really simple. It's important that the compiler knows exactly what code will be run when the interrupt occurs as it then does some very useful optimisation - it is able to inline the callback function and literally inserts the callback function's code at the exact address that is called on a h/w interrupt.

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• Link a programmatic instantiation of class x in class y to a view controller of class x

  - by Joel Derfner

  I have classes Compose and Haiku, each connected to a view controller in IB. Haiku is instantiated in Compose as ghhaiku. Haiku has an array, self.arrayOfHaiku, with 117 members. But in Compose, self.ghhaiku.arrayOfHaiku has no members. I think the problem is that I haven't linked the instance of Haiku that has the 117-member array with the instance of Haiku created in Compose. But how do I do that? (I could of course be totally wrong and the problem could be something else, but that seems to make intuitive sense.) Any thoughts?

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• any way to simplify this with a form of dynamic class instantiation?

  - by gnychis

  I have several child classes that extend a parent class, forced to have a uniform constructor. I have a queue which keeps a list of these classes, which must extend MergeHeuristic. The code that I currently have looks like the following: Class<? extends MergeHeuristic> heuristicRequest = _heuristicQueue.pop(); MergeHeuristic heuristic = null; if(heuristicRequest == AdjacentMACs.class) heuristic = new AdjacentMACs(_parent); if(heuristicRequest == SimilarInterfaceNames.class) heuristic = new SimilarInterfaceNames(_parent); if(heuristicRequest == SameMAC.class) heuristic = new SameMAC(_parent); Is there any way to simplify that to dynamically instantiate the class, something along the lines of: heuristic = new heuristicRequest.somethingSpecial(); That would flatten that block of if statements.

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• ASP.NET MVC - Custom object instantiation / providing with the Modelbinder?

  - by ropstah

  Is it possible to customize the object initiation / providing with the default ASP.NET MVC Modelbinder? <AcceptVerbs(HttpVerbs.Post)> _ Function EditObject(id As int, <Bind(Exclude:="Id")> obj As BLL.Object) As ActionResult End Function I would like to 'provide' obj to the modelbinder. (i don't want the Modelbinder to use New() and instantiate obj, but I want to deliver the object from a custom repository.) Is this possible? Edit: The loading from the repository should be done based on the id parameter of EditObject...

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• Troubleshoot Perl module installation on Mac OS X

  - by Daniel Standage

  I'm trying to install the Perl module Set::IntervalTree on Mac OS X. I recently installed it today on an Ubuntu box with no problem. I simply started cpan, entered install Set:IntervalTree, and it all worked out. However, the installation failed on Mac OS X--it spits out a huge list of compiler errors (below). How would I troubleshoot this. I don't even know where to begin. cpan[1]> install Set::IntervalTree CPAN: Storable loaded ok (v2.18) Going to read /Users/standage/.cpan/Metadata Database was generated on Fri, 14 Jan 2011 02:58:42 GMT CPAN: YAML loaded ok (v0.72) Going to read /Users/standage/.cpan/build/ ............................................................................DONE Found 1 old build, restored the state of 1 Running install for module 'Set::IntervalTree' Running make for B/BE/BENBOOTH/Set-IntervalTree-0.01.tar.gz CPAN: Digest::SHA loaded ok (v5.45) CPAN: Compress::Zlib loaded ok (v2.008) Checksum for /Users/standage/.cpan/sources/authors/id/B/BE/BENBOOTH/Set-IntervalTree-0.01.tar.gz ok Scanning cache /Users/standage/.cpan/build for sizes ............................................................................DONE x Set-IntervalTree-0.01/ x Set-IntervalTree-0.01/src/ x Set-IntervalTree-0.01/src/Makefile x Set-IntervalTree-0.01/src/interval_tree.h x Set-IntervalTree-0.01/src/test_main.cc x Set-IntervalTree-0.01/lib/ x Set-IntervalTree-0.01/lib/Set/ x Set-IntervalTree-0.01/lib/Set/IntervalTree.pm x Set-IntervalTree-0.01/Changes x Set-IntervalTree-0.01/MANIFEST x Set-IntervalTree-0.01/t/ x Set-IntervalTree-0.01/t/Set-IntervalTree.t x Set-IntervalTree-0.01/typemap x Set-IntervalTree-0.01/perlobject.map x Set-IntervalTree-0.01/IntervalTree.xs x Set-IntervalTree-0.01/Makefile.PL x Set-IntervalTree-0.01/README x Set-IntervalTree-0.01/META.yml CPAN: File::Temp loaded ok (v0.18) CPAN.pm: Going to build B/BE/BENBOOTH/Set-IntervalTree-0.01.tar.gz Checking if your kit is complete... Looks good Writing Makefile for Set::IntervalTree cp lib/Set/IntervalTree.pm blib/lib/Set/IntervalTree.pm AutoSplitting blib/lib/Set/IntervalTree.pm (blib/lib/auto/Set/IntervalTree) /usr/bin/perl /System/Library/Perl/5.10.0/ExtUtils/xsubpp -C++ -typemap /System/Library/Perl/5.10.0/ExtUtils/typemap -typemap perlobject.map -typemap typemap IntervalTree.xs > IntervalTree.xsc && mv IntervalTree.xsc IntervalTree.c g++ -c -Isrc -arch x86_64 -arch i386 -arch ppc -g -pipe -fno-common -DPERL_DARWIN -fno-strict-aliasing -I/usr/local/include -g -O0 -DVERSION=\"0.01\" -DXS_VERSION=\"0.01\" "-I/System/Library/Perl/5.10.0/darwin-thread-multi-2level/CORE" -Isrc IntervalTree.c In file included from /usr/include/c++/4.2.1/bits/basic_ios.h:44, from /usr/include/c++/4.2.1/ios:50, from /usr/include/c++/4.2.1/ostream:45, from /usr/include/c++/4.2.1/iostream:45, from IntervalTree.xs:16: /usr/include/c++/4.2.1/bits/locale_facets.h:4420:40: error: macro "do_open" requires 7 arguments, but only 2 given /usr/include/c++/4.2.1/bits/locale_facets.h:4467:34: error: macro "do_close" requires 2 arguments, but only 1 given /usr/include/c++/4.2.1/bits/locale_facets.h:4486:55: error: macro "do_open" requires 7 arguments, but only 2 given /usr/include/c++/4.2.1/bits/locale_facets.h:4513:23: error: macro "do_close" requires 2 arguments, but only 1 given In file included from /usr/include/c++/4.2.1/bits/locale_facets.h:4599, from /usr/include/c++/4.2.1/bits/basic_ios.h:44, from /usr/include/c++/4.2.1/ios:50, from /usr/include/c++/4.2.1/ostream:45, from /usr/include/c++/4.2.1/iostream:45, from IntervalTree.xs:16: /usr/include/c++/4.2.1/i686-apple-darwin10/x86_64/bits/messages_members.h:58:38: error: macro "do_open" requires 7 arguments, but only 2 given /usr/include/c++/4.2.1/i686-apple-darwin10/x86_64/bits/messages_members.h:67:71: error: macro "do_open" requires 7 arguments, but only 2 given /usr/include/c++/4.2.1/i686-apple-darwin10/x86_64/bits/messages_members.h:78:39: error: macro "do_close" requires 2 arguments, but only 1 given In file included from /usr/include/c++/4.2.1/bits/basic_ios.h:44, from /usr/include/c++/4.2.1/ios:50, from /usr/include/c++/4.2.1/ostream:45, from /usr/include/c++/4.2.1/iostream:45, from IntervalTree.xs:16: /usr/include/c++/4.2.1/bits/locale_facets.h:4486: error: ‘do_open’ declared as a ‘virtual’ field /usr/include/c++/4.2.1/bits/locale_facets.h:4486: error: expected ‘;’ before ‘const’ /usr/include/c++/4.2.1/bits/locale_facets.h:4513: error: variable or field ‘do_close’ declared void /usr/include/c++/4.2.1/bits/locale_facets.h:4513: error: expected ‘;’ before ‘const’ In file included from /usr/include/c++/4.2.1/bits/locale_facets.h:4599, from /usr/include/c++/4.2.1/bits/basic_ios.h:44, from /usr/include/c++/4.2.1/ios:50, from /usr/include/c++/4.2.1/ostream:45, from /usr/include/c++/4.2.1/iostream:45, from IntervalTree.xs:16: /usr/include/c++/4.2.1/i686-apple-darwin10/x86_64/bits/messages_members.h:67: error: expected initializer before ‘const’ /usr/include/c++/4.2.1/i686-apple-darwin10/x86_64/bits/messages_members.h:78: error: expected initializer before ‘const’ In file included from IntervalTree.xs:19: src/interval_tree.h:95: error: type/value mismatch at argument 1 in template parameter list for ‘template<class _Tp, class _Alloc> class std::vector’ src/interval_tree.h:95: error: expected a type, got ‘IntervalTree<T,N>::it_recursion_node’ src/interval_tree.h:95: error: template argument 2 is invalid src/interval_tree.h: In constructor ‘IntervalTree<T, N>::IntervalTree()’: src/interval_tree.h:130: error: expected type-specifier src/interval_tree.h:130: error: expected `;' src/interval_tree.h:135: error: expected type-specifier src/interval_tree.h:135: error: expected `;' src/interval_tree.h:141: error: request for member ‘push_back’ in ‘((IntervalTree<T, N>*)this)->IntervalTree<T, N>::recursionNodeStack’, which is of non-class type ‘int’ src/interval_tree.h: In member function ‘void IntervalTree<T, N>::LeftRotate(IntervalTree<T, N>::Node*)’: src/interval_tree.h:178: error: ‘y’ was not declared in this scope src/interval_tree.h: In member function ‘void IntervalTree<T, N>::RightRotate(IntervalTree<T, N>::Node*)’: src/interval_tree.h:240: error: ‘x’ was not declared in this scope src/interval_tree.h: In member function ‘void IntervalTree<T, N>::TreeInsertHelp(IntervalTree<T, N>::Node*)’: src/interval_tree.h:298: error: ‘x’ was not declared in this scope src/interval_tree.h:299: error: ‘y’ was not declared in this scope src/interval_tree.h: In member function ‘typename IntervalTree<T, N>::Node* IntervalTree<T, N>::insert(const T&, N, N)’: src/interval_tree.h:375: error: ‘y’ was not declared in this scope src/interval_tree.h:376: error: ‘x’ was not declared in this scope src/interval_tree.h:377: error: ‘newNode’ was not declared in this scope src/interval_tree.h:379: error: expected type-specifier src/interval_tree.h:379: error: expected `;' src/interval_tree.h: In member function ‘typename IntervalTree<T, N>::Node* IntervalTree<T, N>::GetSuccessorOf(IntervalTree<T, N>::Node*) const’: src/interval_tree.h:450: error: ‘y’ was not declared in this scope src/interval_tree.h: In member function ‘typename IntervalTree<T, N>::Node* IntervalTree<T, N>::GetPredecessorOf(IntervalTree<T, N>::Node*) const’: src/interval_tree.h:483: error: ‘y’ was not declared in this scope src/interval_tree.h: In destructor ‘IntervalTree<T, N>::~IntervalTree()’: src/interval_tree.h:546: error: ‘x’ was not declared in this scope src/interval_tree.h:547: error: type/value mismatch at argument 1 in template parameter list for ‘template<class _Tp, class _Alloc> class std::vector’ src/interval_tree.h:547: error: expected a type, got ‘(IntervalTree<T,N>::Node * <expression error>)’ src/interval_tree.h:547: error: template argument 2 is invalid src/interval_tree.h:547: error: invalid type in declaration before ‘;’ token src/interval_tree.h:551: error: request for member ‘push_back’ in ‘stuffToFree’, which is of non-class type ‘int’ src/interval_tree.h:554: error: request for member ‘push_back’ in ‘stuffToFree’, which is of non-class type ‘int’ src/interval_tree.h:557: error: request for member ‘empty’ in ‘stuffToFree’, which is of non-class type ‘int’ src/interval_tree.h:558: error: request for member ‘back’ in ‘stuffToFree’, which is of non-class type ‘int’ src/interval_tree.h:559: error: request for member ‘pop_back’ in ‘stuffToFree’, which is of non-class type ‘int’ src/interval_tree.h:561: error: request for member ‘push_back’ in ‘stuffToFree’, which is of non-class type ‘int’ src/interval_tree.h:564: error: request for member ‘push_back’ in ‘stuffToFree’, which is of non-class type ‘int’ src/interval_tree.h: In member function ‘void IntervalTree<T, N>::DeleteFixUp(IntervalTree<T, N>::Node*)’: src/interval_tree.h:613: error: ‘w’ was not declared in this scope src/interval_tree.h:614: error: ‘rootLeft’ was not declared in this scope src/interval_tree.h: In member function ‘T IntervalTree<T, N>::remove(IntervalTree<T, N>::Node*)’: src/interval_tree.h:697: error: ‘y’ was not declared in this scope src/interval_tree.h:698: error: ‘x’ was not declared in this scope src/interval_tree.h: In member function ‘std::vector<T, std::allocator<_CharT> > IntervalTree<T, N>::fetch(N, N)’: src/interval_tree.h:819: error: ‘x’ was not declared in this scope src/interval_tree.h:833: error: invalid types ‘int[size_t]’ for array subscript src/interval_tree.h:836: error: request for member ‘push_back’ in ‘((IntervalTree<T, N>*)this)->IntervalTree<T, N>::recursionNodeStack’, which is of non-class type ‘int’ src/interval_tree.h:837: error: request for member ‘back’ in ‘((IntervalTree<T, N>*)this)->IntervalTree<T, N>::recursionNodeStack’, which is of non-class type ‘int’ src/interval_tree.h:838: error: request for member ‘back’ in ‘((IntervalTree<T, N>*)this)->IntervalTree<T, N>::recursionNodeStack’, which is of non-class type ‘int’ src/interval_tree.h:839: error: request for member ‘back’ in ‘((IntervalTree<T, N>*)this)->IntervalTree<T, N>::recursionNodeStack’, which is of non-class type ‘int’ src/interval_tree.h:840: error: request for member ‘size’ in ‘((IntervalTree<T, N>*)this)->IntervalTree<T, N>::recursionNodeStack’, which is of non-class type ‘int’ src/interval_tree.h:846: error: request for member ‘size’ in ‘((IntervalTree<T, N>*)this)->IntervalTree<T, N>::recursionNodeStack’, which is of non-class type ‘int’ src/interval_tree.h:847: error: expected `;' before ‘back’ src/interval_tree.h:848: error: request for member ‘pop_back’ in ‘((IntervalTree<T, N>*)this)->IntervalTree<T, N>::recursionNodeStack’, which is of non-class type ‘int’ src/interval_tree.h:850: error: ‘back’ was not declared in this scope src/interval_tree.h:853: error: invalid types ‘int[size_t]’ for array subscript IntervalTree.c: In function ‘void boot_Set__IntervalTree(PerlInterpreter*, CV*)’: IntervalTree.c:365: warning: deprecated conversion from string constant to ‘char*’ src/interval_tree.h: In constructor ‘IntervalTree<T, N>::IntervalTree() [with T = std::tr1::shared_ptr<sv>, N = long int]’: IntervalTree.c:67: instantiated from here src/interval_tree.h:130: error: cannot convert ‘int*’ to ‘IntervalTree<std::tr1::shared_ptr<sv>, long int>::Node*’ in assignment src/interval_tree.h:135: error: cannot convert ‘int*’ to ‘IntervalTree<std::tr1::shared_ptr<sv>, long int>::Node*’ in assignment ...blah blah blah... ...blah blah blah... ...blah blah blah... ...blah blah blah... ...blah blah blah... ...blah blah blah... src/interval_tree.h:848: error: request for member ‘pop_back’ in ‘((IntervalTree<T, N>*)this)->IntervalTree<T, N>::recursionNodeStack’, which is of non-class type ‘int’ src/interval_tree.h:850: error: ‘back’ was not declared in this scope src/interval_tree.h:853: error: invalid types ‘int[size_t]’ for array subscript IntervalTree.c: In function ‘void boot_Set__IntervalTree(PerlInterpreter*, CV*)’: IntervalTree.c:365: warning: deprecated conversion from string constant to ‘char*’ src/interval_tree.h: In constructor ‘IntervalTree<T, N>::IntervalTree() [with T = std::tr1::shared_ptr<sv>, N = long int]’: IntervalTree.c:67: instantiated from here src/interval_tree.h:130: error: cannot convert ‘int*’ to ‘IntervalTree<std::tr1::shared_ptr<sv>, long int>::Node*’ in assignment src/interval_tree.h:135: error: cannot convert ‘int*’ to ‘IntervalTree<std::tr1::shared_ptr<sv>, long int>::Node*’ in assignment src/interval_tree.h: In member function ‘typename IntervalTree<T, N>::Node* IntervalTree<T, N>::insert(const T&, N, N) [with T = std::tr1::shared_ptr<sv>, N = long int]’: IntervalTree.xs:57: instantiated from here src/interval_tree.h:375: error: dependent-name ‘IntervalTree<T,N>::Node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:375: note: say ‘typename IntervalTree<T,N>::Node’ if a type is meant src/interval_tree.h:376: error: dependent-name ‘IntervalTree<T,N>::Node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:376: note: say ‘typename IntervalTree<T,N>::Node’ if a type is meant src/interval_tree.h:377: error: dependent-name ‘IntervalTree<T,N>::Node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:377: note: say ‘typename IntervalTree<T,N>::Node’ if a type is meant src/interval_tree.h: In member function ‘std::vector<T, std::allocator<_CharT> > IntervalTree<T, N>::fetch(N, N) [with T = std::tr1::shared_ptr<sv>, N = long int]’: IntervalTree.xs:65: instantiated from here src/interval_tree.h:819: error: dependent-name ‘IntervalTree<T,N>::Node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:819: note: say ‘typename IntervalTree<T,N>::Node’ if a type is meant IntervalTree.xs:65: instantiated from here src/interval_tree.h:847: error: dependent-name ‘IntervalTree<T,N>::it_recursion_node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:847: note: say ‘typename IntervalTree<T,N>::it_recursion_node’ if a type is meant src/interval_tree.h: In destructor ‘IntervalTree<T, N>::~IntervalTree() [with T = std::tr1::shared_ptr<sv>, N = long int]’: IntervalTree.c:205: instantiated from here src/interval_tree.h:546: error: dependent-name ‘IntervalTree<T,N>::Node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:546: note: say ‘typename IntervalTree<T,N>::Node’ if a type is meant src/interval_tree.h: In member function ‘void IntervalTree<T, N>::TreeInsertHelp(IntervalTree<T, N>::Node*) [with T = std::tr1::shared_ptr<sv>, N = long int]’: src/interval_tree.h:380: instantiated from ‘typename IntervalTree<T, N>::Node* IntervalTree<T, N>::insert(const T&, N, N) [with T = std::tr1::shared_ptr<sv>, N = long int]’ IntervalTree.xs:57: instantiated from here src/interval_tree.h:298: error: dependent-name ‘IntervalTree<T,N>::Node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:298: note: say ‘typename IntervalTree<T,N>::Node’ if a type is meant src/interval_tree.h:299: error: dependent-name ‘IntervalTree<T,N>::Node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:299: note: say ‘typename IntervalTree<T,N>::Node’ if a type is meant src/interval_tree.h: In member function ‘void IntervalTree<T, N>::LeftRotate(IntervalTree<T, N>::Node*) [with T = std::tr1::shared_ptr<sv>, N = long int]’: src/interval_tree.h:395: instantiated from ‘typename IntervalTree<T, N>::Node* IntervalTree<T, N>::insert(const T&, N, N) [with T = std::tr1::shared_ptr<sv>, N = long int]’ IntervalTree.xs:57: instantiated from here src/interval_tree.h:178: error: dependent-name ‘IntervalTree<T,N>::Node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:178: note: say ‘typename IntervalTree<T,N>::Node’ if a type is meant src/interval_tree.h: In member function ‘void IntervalTree<T, N>::RightRotate(IntervalTree<T, N>::Node*) [with T = std::tr1::shared_ptr<sv>, N = long int]’: src/interval_tree.h:399: instantiated from ‘typename IntervalTree<T, N>::Node* IntervalTree<T, N>::insert(const T&, N, N) [with T = std::tr1::shared_ptr<sv>, N = long int]’ IntervalTree.xs:57: instantiated from here src/interval_tree.h:240: error: dependent-name ‘IntervalTree<T,N>::Node’ is parsed as a non-type, but instantiation yields a type src/interval_tree.h:240: note: say ‘typename IntervalTree<T,N>::Node’ if a type is meant lipo: can't open input file: /var/tmp//ccLthuaw.out (No such file or directory) make: *** [IntervalTree.o] Error 1 BENBOOTH/Set-IntervalTree-0.01.tar.gz make -- NOT OK Running make test Can't test without successful make Running make install Make had returned bad status, install seems impossible Failed during this command: BENBOOTH/Set-IntervalTree-0.01.tar.gz : make NO

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• What makes Erlang suitable for cloud applications?

  - by Duncan

  We are starting a new project and implementing on our corporations's instantiation of an openstack cloud (see http://www.openstack.org/). The project is security tooling for our corporation. We currently run many hundreds of dedicated servers for security tools and are moving them to our corporations instantiation of openstack. Other projects in my company currently use erlang in several distributed server applications, and other Q/A point out erlang is used in several popular cloud services. I am trying to convince others to consider where it might be applicable on our project. What are erlang's strengths for cloud programming? Where are areas it is particularly appropriate to use erlang?

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• Anatomy of a .NET Assembly - Signature encodings

  - by Simon Cooper

  If you've just joined this series, I highly recommend you read the previous posts in this series, starting here, or at least these posts, covering the CLR metadata tables. Before we look at custom attribute encoding, we first need to have a brief look at how signatures are encoded in an assembly in general. Signature types There are several types of signatures in an assembly, all of which share a common base representation, and are all stored as binary blobs in the #Blob heap, referenced by an offset from various metadata tables. The types of signatures are: Method definition and method reference signatures. Field signatures Property signatures Method local variables. These are referenced from the StandAloneSig table, which is then referenced by method body headers. Generic type specifications. These represent a particular instantiation of a generic type. Generic method specifications. Similarly, these represent a particular instantiation of a generic method. All these signatures share the same underlying mechanism to represent a type Representing a type All metadata signatures are based around the ELEMENT_TYPE structure. This assigns a number to each 'built-in' type in the framework; for example, Uint16 is 0x07, String is 0x0e, and Object is 0x1c. Byte codes are also used to indicate SzArrays, multi-dimensional arrays, custom types, and generic type and method variables. However, these require some further information. Firstly, custom types (ie not one of the built-in types). These require you to specify the 4-byte TypeDefOrRef coded token after the CLASS (0x12) or VALUETYPE (0x11) element type. This 4-byte value is stored in a compressed format before being written out to disk (for more excruciating details, you can refer to the CLI specification). SzArrays simply have the array item type after the SZARRAY byte (0x1d). Multidimensional arrays follow the ARRAY element type with a series of compressed integers indicating the number of dimensions, and the size and lower bound of each dimension. Generic variables are simply followed by the index of the generic variable they refer to. There are other additions as well, for example, a specific byte value indicates a method parameter passed by reference (BYREF), and other values indicating custom modifiers. Some examples... To demonstrate, here's a few examples and what the resulting blobs in the #Blob heap will look like. Each name in capitals corresponds to a particular byte value in the ELEMENT_TYPE or CALLCONV structure, and coded tokens to custom types are represented by the type name in curly brackets. A simple field: int intField; FIELD I4 A field of an array of a generic type parameter (assuming T is the first generic parameter of the containing type): T[] genArrayField FIELD SZARRAY VAR 0 An instance method signature (note how the number of parameters does not include the return type): instance string MyMethod(MyType, int&, bool[][]); HASTHIS DEFAULT 3 STRING CLASS {MyType} BYREF I4 SZARRAY SZARRAY BOOLEAN A generic type instantiation: MyGenericType<MyType, MyStruct> GENERICINST CLASS {MyGenericType} 2 CLASS {MyType} VALUETYPE {MyStruct} For more complicated examples, in the following C# type declaration: GenericType<T> : GenericBaseType<object[], T, GenericType<T>> { ... } the Extends field of the TypeDef for GenericType will point to a TypeSpec with the following blob: GENERICINST CLASS {GenericBaseType} 3 SZARRAY OBJECT VAR 0 GENERICINST CLASS {GenericType} 1 VAR 0 And a static generic method signature (generic parameters on types are referenced using VAR, generic parameters on methods using MVAR): TResult[] GenericMethod<TInput, TResult>( TInput, System.Converter<TInput, TOutput>); GENERIC 2 2 SZARRAY MVAR 1 MVAR 0 GENERICINST CLASS {System.Converter} 2 MVAR 0 MVAR 1 As you can see, complicated signatures are recursively built up out of quite simple building blocks to represent all the possible variations in a .NET assembly. Now we've looked at the basics of normal method signatures, in my next post I'll look at custom attribute application signatures, and how they are different to normal signatures.

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• Macro access to members of object where macro is defined

  - by Marc Grue

  Say I have a trait Foo that I instantiate with an initial value val foo = new Foo(6) // class Foo(i: Int) and I later call a second method that in turn calls myMacro foo.secondMethod(7) // def secondMethod(j: Int) = macro myMacro then, how can myMacro find out what my initial value of i (6) is? I didn't succeed with normal compilation reflection using c.prefix, c.eval(...) etc but instead found a 2-project solution: Project B: object CompilationB { def resultB(x: Int, y: Int) = macro resultB_impl def resultB_impl(c: Context)(x: c.Expr[Int], y: c.Expr[Int]) = c.universe.reify(x.splice * y.splice) } Project A (depends on project B): trait Foo { val i: Int // Pass through `i` to compilation B: def apply(y: Int) = CompilationB.resultB(i, y) } object CompilationA { def makeFoo(x: Int): Foo = macro makeFoo_impl def makeFoo_impl(c: Context)(x: c.Expr[Int]): c.Expr[Foo] = c.universe.reify(new Foo {val i = x.splice}) } We can create a Foo and set the i value either with normal instantiation or with a macro like makeFoo. The second approach allows us to customize a Foo at compile time in the first compilation and then in the second compilation further customize its response to input (i in this case)! In some way we get "meta-meta" capabilities (or "pataphysic"-capabilities ;-) Normally we would need to have foo in scope to introspect i (with for instance c.eval(...)). But by saving the i value inside the Foo object we can access it anytime and we could instantiate Foo anywhere: object Test extends App { import CompilationA._ // Normal instantiation val foo1 = new Foo {val i = 7} val r1 = foo1(6) // Macro instantiation val foo2 = makeFoo(7) val r2 = foo2(6) // "Curried" invocation val r3 = makeFoo(6)(7) println(s"Result 1 2 3: $r1 $r2 $r3") assert((r1, r2, r3) ==(42, 42, 42)) } My question Can I find i inside my example macros without this double compilation hackery?

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• IList<Item> Collection Class accessing database

  - by Mike

  Hi, I have a database with Users. Users have Items. These Items can change actively. How do you access the items in a collection type format? For the user, I fill all the user properties at the time of instantiation. If I load the user's items at the time of the instantiation, and the items change, they will have old data. I was thinking, maybe I need an ItemCollection class and have that a field/property apart of the user class, that way to traverse all the user's items I could use a foreach loop. So, my question is, what is the best practice/best way of accessing the items from a database using some sort of collection? On accessing the particular Item, it needs to get the latest database information, and when the user does do a foreach loop, the latest item information must be available. I.e. What I'm trying to do Console.WriteLine(User.Items[3].ID); returns 5. //this updates the item information and saves it to the database. User.Items[3].ID = 13; //Add a new item to the database. User.Items.Add(new Item { id = 17}); foreach (Item item in User.Items) { //this would traverse all items in the database. //not some cached copy at the time of instantiation of the user. }

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• Template inheritence c++

  - by Chris Condy

  I have made a template singleton class, I have also made a data structure that is templated. My question is; how do I make my templated data structure inherit from a singleton so you can only have one float type of this structure? I have tested both seperate and have found no problems. Code provided under... (That is the problem) template <class Type> class AbstractRManagers : public Singleton<AbstractRManagers<Type> > The problem is the code above doesn't work I get alot of errors. I cant get it to no matter what I do template a templated singleton class... I was asking for maybe advice or maybe if the code above is incorrect guidence? #ifndef SINGLETON_H #define SINGLETON_H template <class Type> class Singleton { public: virtual ~Singleton(); Singleton(); static Type* m_instance; }; template <class Type> Type* Singleton<Type>::m_instance = 0; #include "Singleton.cpp" #endif #ifndef SINGLETON_CPP #define SINGLETON_CPP #include "Singleton.h" template <class Type> Singleton<Type>::Singleton() { } template <class Type> Singleton<Type>::~Singleton() { } template <class Type> Type* Singleton<Type>::getInstance() { if(m_instance==nullptr) { m_instance = new Type; } return m_instance; } #endif #ifndef ABSTRACTRMANAGERS_H #define ABSTRACTRMANAGERS_H #include <vector> #include <map> #include <stack> #include "Singleton.h" template <class Type> class AbstractRManagers : public Singleton<AbstractRManagers<Type> > { public: virtual ~AbstractRManagers(); int insert(Type* type, std::string name); Type* remove(int i); Type* remove(std::string name); Type* get(int i); Type* getS(std::string name); int get(std::string name); int get(Type* i); bool check(std::string name); int resourceSize(); protected: private: std::vector<Type*> m_resources; std::map<std::string,int> m_map; std::stack<int> m_freePos; }; #include "AbstractRManagers.cpp" #endif #ifndef ABSTRACTRMANAGERS_CPP #define ABSTRACTRMANAGERS_CPP #include "AbstractRManagers.h" template <class Type> int AbstractRManagers<Type>::insert(Type* type, std::string name) { int i=0; if(!check(name)) { if(m_freePos.empty()) { m_resources.push_back(type); i = m_resources.size()-1; m_map[name] = i; } else { i = m_freePos.top(); m_freePos.pop(); m_resources[i] = type; m_map[name] = i; } } else i = -1; return i; } template <class Type> int AbstractRManagers<Type>::resourceSize() { return m_resources.size(); } template <class Type> bool AbstractRManagers<Type>::check(std::string name) { std::map<std::string,int>::iterator it; it = m_map.find(name); if(it==m_map.end()) return false; return true; } template <class Type> Type* AbstractRManagers<Type>::remove(std::string name) { Type* temp = m_resources[m_map[name]]; if(temp!=NULL) { std::map<std::string,int>::iterator it; it = m_map[name]; m_resources[m_map[name]] = NULL; m_freePos.push(m_map[name]); delete (*it).second; delete (*it).first; return temp; } return NULL; } template <class Type> Type* AbstractRManagers<Type>::remove(int i) { if((i < m_resources.size())&&(i > 0)) { Type* temp = m_resources[i]; m_resources[i] = NULL; m_freePos.push(i); std::map<std::string,int>::iterator it; for(it=m_map.begin();it!=m_map.end();it++) { if((*it).second == i) { delete (*it).second; delete (*it).first; return temp; } } return temp; } return NULL; } template <class Type> int AbstractRManagers<Type>::get(Type* i) { for(int i2=0;i2<m_resources.size();i2++) { if(i == m_resources[i2]) { return i2; } } return -1; } template <class Type> Type* AbstractRManagers<Type>::get(int i) { if((i < m_resources.size())&&(i >= 0)) { return m_resources[i]; } return NULL; } template <class Type> Type* AbstractRManagers<Type>::getS(std::string name) { return m_resources[m_map[name]]; } template <class Type> int AbstractRManagers<Type>::get(std::string name) { return m_map[name]; } template <class Type> AbstractRManagers<Type>::~AbstractRManagers() { } #endif #include "AbstractRManagers.h" struct b { float x; }; int main() { b* a = new b(); AbstractRManagers<b>::getInstance()->insert(a,"a"); return 0; } This program produces next errors when compiled : 1> main.cpp 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::stack<_Ty,_Container> &,const std::stack<_Ty,_Container> &)' : could not deduce template argument for 'const std::stack<_Ty,_Container> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\stack(166) : see declaration of 'std::operator <' 1> c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(124) : while compiling class template member function 'bool std::less<_Ty>::operator ()(const _Ty &,const _Ty &) const' 1> with 1> [ 1> _Ty=std::string 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\map(71) : see reference to class template instantiation 'std::less<_Ty>' being compiled 1> with 1> [ 1> _Ty=std::string 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(451) : see reference to class template instantiation 'std::_Tmap_traits<_Kty,_Ty,_Pr,_Alloc,_Mfl>' being compiled 1> with 1> [ 1> _Kty=std::string, 1> _Ty=int, 1> _Pr=std::less<std::string>, 1> _Alloc=std::allocator<std::pair<const std::string,int>>, 1> _Mfl=false 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(520) : see reference to class template instantiation 'std::_Tree_nod<_Traits>' being compiled 1> with 1> [ 1> _Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::allocator<std::pair<const std::string,int>>,false> 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(659) : see reference to class template instantiation 'std::_Tree_val<_Traits>' being compiled 1> with 1> [ 1> _Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::allocator<std::pair<const std::string,int>>,false> 1> ] 1> c:\program files\microsoft visual studio 10.0\vc\include\map(81) : see reference to class template instantiation 'std::_Tree<_Traits>' being compiled 1> with 1> [ 1> _Traits=std::_Tmap_traits<std::string,int,std::less<std::string>,std::allocator<std::pair<const std::string,int>>,false> 1> ] 1> c:\users\chris\desktop\311\ideas\idea1\idea1\abstractrmanagers.h(28) : see reference to class template instantiation 'std::map<_Kty,_Ty>' being compiled 1> with 1> [ 1> _Kty=std::string, 1> _Ty=int 1> ] 1> c:\users\chris\desktop\311\ideas\idea1\idea1\abstractrmanagers.h(30) : see reference to class template instantiation 'AbstractRManagers<Type>' being compiled 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::stack<_Ty,_Container> &,const std::stack<_Ty,_Container> &)' : could not deduce template argument for 'const std::stack<_Ty,_Container> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\stack(166) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::stack<_Ty,_Container> &,const std::stack<_Ty,_Container> &)' : could not deduce template argument for 'const std::stack<_Ty,_Container> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\stack(166) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::deque<_Ty,_Alloc> &,const std::deque<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::deque<_Ty,_Alloc> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\deque(1725) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::deque<_Ty,_Alloc> &,const std::deque<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::deque<_Ty,_Alloc> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\deque(1725) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::deque<_Ty,_Alloc> &,const std::deque<_Ty,_Alloc> &)' : could not deduce template argument for 'const std::deque<_Ty,_Alloc> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\deque(1725) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(1885) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(1885) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Tree<_Traits> &,const std::_Tree<_Traits> &)' : could not deduce template argument for 'const std::_Tree<_Traits> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xtree(1885) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\vector(1502) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\vector(1502) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::vector<_Ty,_Ax> &,const std::vector<_Ty,_Ax> &)' : could not deduce template argument for 'const std::vector<_Ty,_Ax> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\vector(1502) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\memory(2582) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\memory(2582) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::unique_ptr<_Ty,_Dx> &,const std::unique_ptr<_Ty2,_Dx2> &)' : could not deduce template argument for 'const std::unique_ptr<_Ty,_Dx> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\memory(2582) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1356) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1356) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::reverse_iterator<_RanIt> &,const std::reverse_iterator<_RanIt2> &)' : could not deduce template argument for 'const std::reverse_iterator<_RanIt> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1356) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1179) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1179) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::_Revranit<_RanIt,_Base> &,const std::_Revranit<_RanIt2,_Base2> &)' : could not deduce template argument for 'const std::_Revranit<_RanIt,_Base> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\xutility(1179) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(318) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(318) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2784: 'bool std::operator <(const std::pair<_Ty1,_Ty2> &,const std::pair<_Ty1,_Ty2> &)' : could not deduce template argument for 'const std::pair<_Ty1,_Ty2> &' from 'const std::string' 1> c:\program files\microsoft visual studio 10.0\vc\include\utility(318) : see declaration of 'std::operator <' 1>c:\program files\microsoft visual studio 10.0\vc\include\xfunctional(125): error C2676: binary '<' : 'const std::string' does not define this operator or a conversion to a type acceptable to the predefined operator ========== Build: 0 succeeded, 1 failed, 0 up-to-date, 0 skipped ==========

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• How can I resize a set of sprite images?

  - by Tyler J Fisher

  Hey StackExchange GameDev community, I'm attempting to resize series of sprites upon instantiation of the class they're located in. I've attempted to use the following code to resize the images, however my attempts have been unsuccessful. I have been unable to write an implementation that is even compilable, so no error codes yet. wLeft.getScaledInstance(wLeft.getWidth()*2, wLeft.getHeight()*2, Image.SCALE_FAST); I've heard that Graphics2D is the best option. Any suggestions? I think I'm probably best off loading the images into a Java project, resizing the images then outputting them to a new directory so as not to have to resize each sprite upon class instantiation. What do you think? Photoshopping each individual sprite is out of the question, unless I used a macro. Code: package game; //Import import java.awt.Image; import javax.swing.ImageIcon; public class Mario extends Human { Image wLeft = new ImageIcon("sprites\\mario\\wLeft.PNG").getImage(); //Constructor public Mario(){ super("Mario", 50); wLeft = wLeft.getScaledInstance(wLeft.getWidth()*2, wLeft.getHeight()*2, Image.SCALE_FAST); }

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• Did 12.04 just add multi-touch gesture support mid-release?

  - by adempewolff

  I was reviewing the updates I was about to download today and I noticed that a lot of them had to do with gesture support, noticed that many of these were new installs rather than upgrades. Has 12.04 just added multi-touch gesture support mid-release? If so, what are the capabilities that this adds? Which applications already support these capabilities and can I expect others to add support in the near future? Here are the packages that were installed: Install: libframe6:amd64 (2.2.4-0ubuntu0.12.04.1), libgeis1:amd64 (2.2.9.2-0ubuntu1), libgrail5:amd64 (3.0.6-0ubuntu0.12.04.01, automatic) And here are those that were upgraded (also including many with touch support): Upgrade: libgrip0:amd64 (0.3.4-0ubuntu2~ubuntu12.04.1, 0.3.5-0ubuntu1~12.04.1), eog:amd64 (3.4.2-0ubuntu1, 3.4.2-0ubuntu1.1), ginn:amd64 (0.2.4-0ubuntu1, 0.2.4.1-0ubuntu1) Of which the descriptions for the new installs are, libgeis1: Gesture engine interface support A common API for clients of a systemwide gesture recognition and propagation engine. libframe6: Touch Frame Library This library handles the buildup and synchronization of a set of simultaneous touches. The library is input agnostic, with bindings for mtdev, frame and XI2.1. libgrail5: Gesture Recognition And Instantiation Library This library consists of an interface and tools for handling gesture recognition and gesture instantiation. Applications can use the grail callbacks to receive gesture primitives and raw input events from the underlying kernel device. And the descriptions for the upgraded packages are, ligrip0: provides multitouch gestures to GTK+ apps Libgrip hooks gesture recognition into GTK+ applications. ginn: Gesture Injector: No-GEIS, No-Toolkits A daemon with jinn-like wish-granting capabilities: it gives applications the ability to support a subset of multi-touch gestures without having to integrate GEIS or multi-touch GTK/Qt libs. Adding in a ton of new libraries and upgrading the existing components makes me wonder if 12.04 is meant to start natively supporting gestures other than two finger scroll in the near future. I expected these capabilities to be introduced soon but I thought that they would only be rolled out in a new release, not as upgrades for an existing release. Anyone have any info about this?

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• Variant Management– Which Approach fits for my Product?

  - by C. Chadwick

  Jürgen Kunz – Director Product Development – Oracle ORACLE Deutschland B.V. & Co. KG Introduction In a difficult economic environment, it is important for companies to understand the customer requirements in detail and to address them in their products. Customer specific products, however, usually cause increased costs. Variant management helps to find the best combination of standard components and custom components which balances customer’s product requirements and product costs. Depending on the type of product, different approaches to variant management will be applied. For example the automotive product “car” or electronic/high-tech products like a “computer”, with a pre-defined set of options to be combined in the individual configuration (so called “Assembled to Order” products), require a different approach to products in heavy machinery, which are (at least partially) engineered in a customer specific way (so-called “Engineered-to Order” products). This article discusses different approaches to variant management. Starting with the simple Bill of Material (BOM), this article presents three different approaches to variant management, which are provided by Agile PLM. Single level BOM and Variant BOM The single level BOM is the basic form of the BOM. The product structure is defined using assemblies and single parts. A particular product is thus represented by a fixed product structure. As soon as you have to manage product variants, the single level BOM is no longer sufficient. A variant BOM will be needed to manage product variants. The variant BOM is sometimes referred to as 150% BOM, since a variant BOM contains more parts and assemblies than actually needed to assemble the (final) product – just 150% of the parts You can evolve the variant BOM from the single level BOM by replacing single nodes with a placeholder node. The placeholder in this case represents the possible variants of a part or assembly. Product structure nodes, which are part of any product, are so-called “Must-Have” parts. “Optional” parts can be omitted in the final product. Additional attributes allow limiting the quantity of parts/assemblies which can be assigned at a certain position in the Variant BOM. Figure 1 shows the variant BOM of Agile PLM. Figure 1 Variant BOM in Agile PLM During the instantiation of the Variant BOM, the placeholders get replaced by specific variants of the parts and assemblies. The selection of the desired or appropriate variants is either done step by step by the user or by applying pre-defined configuration rules. As a result of the instantiation, an independent BOM will be created (Figure 2). Figure 2 Instantiated BOM in Agile PLM This kind of Variant BOM  can be used for „Assembled –To-Order“ type products as well as for „Engineered-to-Order“-type products. In case of “Assembled –To-Order” type products, typically the instantiation is done automatically with pre-defined configuration rules. For „Engineered- to-Order“-type products at least part of the product is selected manually to make use of customized parts/assemblies, that have been engineered according to the specific custom requirements. Template BOM The Template BOM is used for „Engineered-to-Order“-type products. It is another type of variant BOM. The engineer works in a flexible environment which allows him to build the most creative solutions. At the same time the engineer shall be guided to re-use existing solutions and it shall be assured that product variants of the same product family share the same base structure. The template BOM defines the basic structure of products belonging to the same product family. Let’s take a gearbox as an example. The customer specific configuration of the gearbox is influenced by several parameters (e.g. rpm range, transmitted torque), which are defined in the customer’s requirement document.  Figure 3 shows part of a Template BOM (yellow) and its relation to the product family hierarchy (blue).  Figure 3 Template BOM Every component of the Template BOM has links to the variants that have been engineeried so far for the component (depending on the level in the Template BOM, they are product variants, Assembly Variant or single part variants). This library of solutions, the so-called solution space, can be used by the engineers to build new product variants. In the best case, the engineer selects an existing solution variant, such as the gearbox shown in figure 3. When the existing variants do not fulfill the specific requirements, a new variant will be engineered. This new variant must be compliant with the given Template BOM. If we look at the gearbox in figure 3  it must consist of a transmission housing, a Connecting Plate, a set of Gears and a Planetary transmission – pre-assumed that all components are must have components. The new variant will enhance the solution space and is automatically available for re-use in future variants. The result of the instantiation of the Template BOM is a stand-alone BOM which represents the customer specific product variant. Modular BOM The concept of the modular BOM was invented in the automotive industry. Passenger cars are so-called „Assembled-to-Order“-products. The customer first selects the specific equipment of the car (so-called specifications) – for instance engine, audio equipment, rims, color. Based on this information the required parts will be determined and the customer specific car will be assembled. Certain combinations of specification are not available for the customer, because they are not feasible from technical perspective (e.g. a convertible with sun roof) or because the combination will not be offered for marketing reasons (e.g. steel rims with a sports line car). The modular BOM (yellow structure in figure 4) is defined in the context of a specific product family (in the sample it is product family „Speedstar“). It is the same modular BOM for the different types of cars of the product family (e.g. sedan, station wagon). The assembly or single parts of the car (blue nodes in figure 4) are assigned at the leaf level of the modular BOM. The assignment of assembly and parts to the modular BOM is enriched with a configuration rule (purple elements in figure 4). The configuration rule defines the conditions to use a specific assembly or single part. The configuration rule is valid in the context of a type of car (green elements in figure 4). Color specific parts are assigned to the color independent parts via additional configuration rules (grey elements in figure 4). The configuration rules use Boolean operators to connect the specifications. Additional consistency rules (constraints) may be used to define invalid combinations of specification (so-called exclusions). Furthermore consistency rules may be used to add specifications to the set of specifications. For instance it is important that a car with diesel engine always is build using the high capacity battery.  Figure 4 Modular BOM The calculation of the car configuration consists of several steps. First the consistency rules (constraints) are applied. Resulting from that specification might be added automatically. The second step will determine the assemblies and single parts for the complete structure of the modular BOM, by evaluating the configuration rules in the context of the current type of car. The evaluation of the rules for one component in the modular BOM might result in several rules being fulfilled. In this case the most specific rule (typically the longest rule) will win. Thanks to this approach, it is possible to add a specific variant to the modular BOM without the need to change any other configuration rules.  As a result the whole set of configuration rules is easy to maintain. Finally the color specific assemblies respective parts will be determined and the configuration is completed. Figure 5 Calculated Car Configuration The result of the car configuration is shown in figure 5. It shows the list of assemblies respective single parts (blue components in figure 5), which are required to build the customer specific car. Summary There are different approaches to variant management. Three different approaches have been presented in this article. At the end of the day, it is the type of the product which decides about the best approach.  For „Assembled to Order“-type products it is very likely that you can define the configuration rules and calculate the product variant automatically. Products of type „Engineered-to-Order“ ,however, need to be engineered. Nevertheless in the majority of cases, part of the product structure can be generated automatically in a similar way to „Assembled to Order“-tape products.  That said it is important first to analyze the product portfolio, in order to define the best approach to variant management.

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• What is a good way to share internal helpers?

  - by toplel32

  All my projects share the same base library that I have build up over quite some time. It contains utilities and static helper classes to assist them where .NET doesn't exactly offer what I want. Originally all the helpers were written mainly to serve an internal purpose and it has to stay that way, but sometimes they prove very useful to other assemblies. Now making them public in a reliable way is more complicated than most would think, for example all methods that assume nullable types must now contain argument checking while not charging internal utilities with the price of doing so. The price might be negligible, but it is far from right. While refactoring, I have revised this case multiple times and I've come up with the following solutions so far: Have an internal and public class for each helper The internal class contains the actual code while the public class serves as an access point which does argument checking. Cons: The internal class requires a prefix to avoid ambiguity (the best presentation should be reserved for public types) It isn't possible to discriminate methods that don't need argument checking   Have one class that contains both internal and public members (as conventionally implemented in .NET framework). At first, this might sound like the best possible solution, but it has the same first unpleasant con as solution 1. Cons: Internal methods require a prefix to avoid ambiguity   Have an internal class which is implemented by the public class that overrides any members that require argument checking. Cons: Is non-static, atleast one instantiation is required. This doesn't really fit into the helper class idea, since it generally consists of independent fragments of code, it should not require instantiation. Non-static methods are also slower by a negligible degree, which doesn't really justify this option either. There is one general and unavoidable consequence, alot of maintenance is necessary because every internal member will require a public counterpart. A note on solution 1: The first consequence can be avoided by putting both classes in different namespaces, for example you can have the real helper in the root namespace and the public helper in a namespace called "Helpers".

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• C++: Trouble with templates (C2064)

  - by Rosarch

  I'm having compiler errors, and I'm not sure why. What am I doing wrong here: Hangman.cpp: set<char> Hangman::incorrectGuesses() { // Hangman line 103 return Utils::findAll_if<char>(guesses.begin(), guesses.end(), &Hangman::isIncorrectGuess); } bool Hangman::isIncorrectGuess(char c) { return correctAnswer.find(c) == string::npos; } Utils.h: namespace Utils { void PrintLine(const string& line, int tabLevel = 0); string getTabs(int tabLevel); template<class result_t, class Predicate> std::set<result_t> findAll_if(typename std::set<result_t>::iterator begin, typename std::set<result_t>::iterator end, Predicate pred) { std::set<result_t> result; // utils line 16 return detail::findAll_if_rec<result_t>(begin, end, pred, result); } } namespace detail { template<class result_t, class Predicate> std::set<result_t> findAll_if_rec(typename std::set<result_t>::iterator begin, typename std::set<result_t>::iterator end, Predicate pred, std::set<result_t> result) { // utils line 25 typename std::set<result_t>::iterator nextResultElem = find_if(begin, end, pred); if (nextResultElem == end) { return result; } result.insert(*nextResultElem); return findAll_if_rec(++nextResultElem, end, pred, result); } } This produces the following compiler errors: algorithm(83): error C2064: term does not evaluate to a function taking 1 arguments algorithm(95) : see reference to function template instantiation '_InIt std::_Find_if<std::_Tree_unchecked_const_iterator<_Mytree>,_Pr>(_InIt,_InIt,_Pr)' being compiled 1> with 1> [ 1> _InIt=std::_Tree_unchecked_const_iterator<std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>>, 1> _Mytree=std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>, 1> _Pr=bool (__thiscall Hangman::* )(char) 1> ] utils.h(25) : see reference to function template instantiation '_InIt std::find_if<std::_Tree_const_iterator<_Mytree>,Predicate>(_InIt,_InIt,_Pr)' being compiled 1> with 1> [ 1> _InIt=std::_Tree_const_iterator<std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>>, 1> _Mytree=std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>, 1> Predicate=bool (__thiscall Hangman::* )(char), 1> _Pr=bool (__thiscall Hangman::* )(char) 1> ] utils.h(16) : see reference to function template instantiation 'std::set<_Kty> detail::findAll_if_rec<result_t,Predicate>(std::_Tree_const_iterator<_Mytree>,std::_Tree_const_iterator<_Mytree>,Predicate,std::set<_Kty>)' being compiled 1> with 1> [ 1> _Kty=char, 1> result_t=char, 1> Predicate=bool (__thiscall Hangman::* )(char), 1> _Mytree=std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>> 1> ] hangman.cpp(103) : see reference to function template instantiation 'std::set<_Kty> Utils::findAll_if<char,bool(__thiscall Hangman::* )(char)>(std::_Tree_const_iterator<_Mytree>,std::_Tree_const_iterator<_Mytree>,Predicate)' being compiled 1> with 1> [ 1> _Kty=char, 1> _Mytree=std::_Tree_val<std::_Tset_traits<char,std::less<char>,std::allocator<char>,false>>, 1> Predicate=bool (__thiscall Hangman::* )(char) 1> ]

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• std::basic_string full specialization (g++ conflict)

  - by SoapBox

  I am trying to define a full specialization of std::basic_string< char, char_traits<char>, allocator<char> > which is typedef'd (in g++) by the <string> header. The problem is, if I include <string> first, g++ sees the typedef as an instantiation of basic_string and gives me errors. If I do my specialization first then I have no issues. I should be able to define my specialization after <string> is included. What do I have to do to be able to do that? My Code: #include <bits/localefwd.h> //#include <string> // <- uncommenting this line causes compilation to fail namespace std { template<> class basic_string< char, char_traits<char>, allocator<char> > { public: int blah() { return 42; } size_t size() { return 0; } const char *c_str() { return ""; } void reserve(int) {} void clear() {} }; } #include <string> #include <iostream> int main() { std::cout << std::string().blah() << std::endl; } The above code works fine. But, if I uncomment the first #include <string> line, I get the following compiler errors: blah.cpp:7: error: specialization of ‘std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ after instantiation blah.cpp:7: error: redefinition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ /usr/include/c++/4.4/bits/stringfwd.h:52: error: previous definition of ‘class std::basic_string<char, std::char_traits<char>, std::allocator<char> >’ blah.cpp: In function ‘int main()’: blah.cpp:22: error: ‘class std::string’ has no member named ‘blah’ Line 52 of /usr/include/c++/4.4/bits/stringfwd.h: template<typename _CharT, typename _Traits = char_traits<_CharT>, typename _Alloc = allocator<_CharT> > class basic_string; As far as I know this is just a forward delcaration of the template, NOT an instantiation as g++ claims. Line 56 of /usr/include/c++/4.4/bits/stringfwd.h: typedef basic_string<char> string; As far as I know this is just a typedef, NOT an instantiation either. So why are these lines conflicting with my code? What can I do to fix this other than ensuring that my code is always included before <string>?

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• C#: System.Lazy&lt;T&gt; and the Singleton Design Pattern

  - by James Michael Hare

  So we've all coded a Singleton at one time or another.  It's a really simple pattern and can be a slightly more elegant alternative to global variables.  Make no mistake, Singletons can be abused and are often over-used -- but occasionally you find a Singleton is the most elegant solution. For those of you not familiar with a Singleton, the basic Design Pattern is that a Singleton class is one where there is only ever one instance of the class created.  This means that constructors must be private to avoid users creating their own instances, and a static property (or method in languages without properties) is defined that returns a single static instance. 1: public class Singleton 2: { 3: // the single instance is defined in a static field 4: private static readonly Singleton _instance = new Singleton(); 5:  6: // constructor private so users can't instantiate on their own 7: private Singleton() 8: { 9: } 10:  11: // read-only property that returns the static field 12: public static Singleton Instance 13: { 14: get 15: { 16: return _instance; 17: } 18: } 19: } This is the most basic singleton, notice the key features: Static readonly field that contains the one and only instance. Constructor is private so it can only be called by the class itself. Static property that returns the single instance. Looks like it satisfies, right?  There's just one (potential) problem.  C# gives you no guarantee of when the static field _instance will be created.  This is because the C# standard simply states that classes (which are marked in the IL as BeforeFieldInit) can have their static fields initialized any time before the field is accessed.  This means that they may be initialized on first use, they may be initialized at some other time before, you can't be sure when. So what if you want to guarantee your instance is truly lazy.  That is, that it is only created on first call to Instance?  Well, there's a few ways to do this.  First we'll show the old ways, and then talk about how .Net 4.0's new System.Lazy<T> type can help make the lazy-Singleton cleaner. Obviously, we could take on the lazy construction ourselves, but being that our Singleton may be accessed by many different threads, we'd need to lock it down. 1: public class LazySingleton1 2: { 3: // lock for thread-safety laziness 4: private static readonly object _mutex = new object(); 5:  6: // static field to hold single instance 7: private static LazySingleton1 _instance = null; 8:  9: // property that does some locking and then creates on first call 10: public static LazySingleton1 Instance 11: { 12: get 13: { 14: if (_instance == null) 15: { 16: lock (_mutex) 17: { 18: if (_instance == null) 19: { 20: _instance = new LazySingleton1(); 21: } 22: } 23: } 24:  25: return _instance; 26: } 27: } 28:  29: private LazySingleton1() 30: { 31: } 32: } This is a standard double-check algorithm so that you don't lock if the instance has already been created.  However, because it's possible two threads can go through the first if at the same time the first time back in, you need to check again after the lock is acquired to avoid creating two instances. Pretty straightforward, but ugly as all heck.  Well, you could also take advantage of the C# standard's BeforeFieldInit and define your class with a static constructor.  It need not have a body, just the presence of the static constructor will remove the BeforeFieldInit attribute on the class and guarantee that no fields are initialized until the first static field, property, or method is called.   1: public class LazySingleton2 2: { 3: // because of the static constructor, this won't get created until first use 4: private static readonly LazySingleton2 _instance = new LazySingleton2(); 5:  6: // Returns the singleton instance using lazy-instantiation 7: public static LazySingleton2 Instance 8: { 9: get { return _instance; } 10: } 11:  12: // private to prevent direct instantiation 13: private LazySingleton2() 14: { 15: } 16:  17: // removes BeforeFieldInit on class so static fields not 18: // initialized before they are used 19: static LazySingleton2() 20: { 21: } 22: } Now, while this works perfectly, I hate it.  Why?  Because it's relying on a non-obvious trick of the IL to guarantee laziness.  Just looking at this code, you'd have no idea that it's doing what it's doing.  Worse yet, you may decide that the empty static constructor serves no purpose and delete it (which removes your lazy guarantee).  Worse-worse yet, they may alter the rules around BeforeFieldInit in the future which could change this. So, what do I propose instead?  .Net 4.0 adds the System.Lazy type which guarantees thread-safe lazy-construction.  Using System.Lazy<T>, we get: 1: public class LazySingleton3 2: { 3: // static holder for instance, need to use lambda to construct since constructor private 4: private static readonly Lazy<LazySingleton3> _instance 5: = new Lazy<LazySingleton3>(() => new LazySingleton3()); 6:  7: // private to prevent direct instantiation. 8: private LazySingleton3() 9: { 10: } 11:  12: // accessor for instance 13: public static LazySingleton3 Instance 14: { 15: get 16: { 17: return _instance.Value; 18: } 19: } 20: } Note, you need your lambda to call the private constructor as Lazy's default constructor can only call public constructors of the type passed in (which we can't have by definition of a Singleton).  But, because the lambda is defined inside our type, it has access to the private members so it's perfect. Note how the Lazy<T> makes it obvious what you're doing (lazy construction), instead of relying on an IL generation side-effect.  This way, it's more maintainable.  Lazy<T> has many other uses as well, obviously, but I really love how elegant and readable it makes the lazy Singleton.

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• Subterranean IL: The ThreadLocal type

  - by Simon Cooper

  I came across ThreadLocal<T> while I was researching ConcurrentBag. To look at it, it doesn't really make much sense. What's all those extra Cn classes doing in there? Why is there a GenericHolder<T,U,V,W> class? What's going on? However, digging deeper, it's a rather ingenious solution to a tricky problem. Thread statics Declaring that a variable is thread static, that is, values assigned and read from the field is specific to the thread doing the reading, is quite easy in .NET: [ThreadStatic] private static string s_ThreadStaticField; ThreadStaticAttribute is not a pseudo-custom attribute; it is compiled as a normal attribute, but the CLR has in-built magic, activated by that attribute, to redirect accesses to the field based on the executing thread's identity. TheadStaticAttribute provides a simple solution when you want to use a single field as thread-static. What if you want to create an arbitary number of thread static variables at runtime? Thread-static fields can only be declared, and are fixed, at compile time. Prior to .NET 4, you only had one solution - thread local data slots. This is a lesser-known function of Thread that has existed since .NET 1.1: LocalDataStoreSlot threadSlot = Thread.AllocateNamedDataSlot("slot1"); string value = "foo"; Thread.SetData(threadSlot, value); string gettedValue = (string)Thread.GetData(threadSlot); Each instance of LocalStoreDataSlot mediates access to a single slot, and each slot acts like a separate thread-static field. As you can see, using thread data slots is quite cumbersome. You need to keep track of LocalDataStoreSlot objects, it's not obvious how instances of LocalDataStoreSlot correspond to individual thread-static variables, and it's not type safe. It's also relatively slow and complicated; the internal implementation consists of a whole series of classes hanging off a single thread-static field in Thread itself, using various arrays, lists, and locks for synchronization. ThreadLocal<T> is far simpler and easier to use. ThreadLocal ThreadLocal provides an abstraction around thread-static fields that allows it to be used just like any other class; it can be used as a replacement for a thread-static field, it can be used in a List<ThreadLocal<T>>, you can create as many as you need at runtime. So what does it do? It can't just have an instance-specific thread-static field, because thread-static fields have to be declared as static, and so shared between all instances of the declaring type. There's something else going on here. The values stored in instances of ThreadLocal<T> are stored in instantiations of the GenericHolder<T,U,V,W> class, which contains a single ThreadStatic field (s_value) to store the actual value. This class is then instantiated with various combinations of the Cn types for generic arguments. In .NET, each separate instantiation of a generic type has its own static state. For example, GenericHolder<int,C0,C1,C2> has a completely separate s_value field to GenericHolder<int,C1,C14,C1>. This feature is (ab)used by ThreadLocal to emulate instance thread-static fields. Every time an instance of ThreadLocal is constructed, it is assigned a unique number from the static s_currentTypeId field using Interlocked.Increment, in the FindNextTypeIndex method. The hexadecimal representation of that number then defines the specific Cn types that instantiates the GenericHolder class. That instantiation is therefore 'owned' by that instance of ThreadLocal. This gives each instance of ThreadLocal its own ThreadStatic field through a specific unique instantiation of the GenericHolder class. Although GenericHolder has four type variables, the first one is always instantiated to the type stored in the ThreadLocal<T>. This gives three free type variables, each of which can be instantiated to one of 16 types (C0 to C15). This puts an upper limit of 4096 (163) on the number of ThreadLocal<T> instances that can be created for each value of T. That is, there can be a maximum of 4096 instances of ThreadLocal<string>, and separately a maximum of 4096 instances of ThreadLocal<object>, etc. However, there is an upper limit of 16384 enforced on the total number of ThreadLocal instances in the AppDomain. This is to stop too much memory being used by thousands of instantiations of GenericHolder<T,U,V,W>, as once a type is loaded into an AppDomain it cannot be unloaded, and will continue to sit there taking up memory until the AppDomain is unloaded. The total number of ThreadLocal instances created is tracked by the ThreadLocalGlobalCounter class. So what happens when either limit is reached? Firstly, to try and stop this limit being reached, it recycles GenericHolder type indexes of ThreadLocal instances that get disposed using the s_availableIndices concurrent stack. This allows GenericHolder instantiations of disposed ThreadLocal instances to be re-used. But if there aren't any available instantiations, then ThreadLocal falls back on a standard thread local slot using TLSHolder. This makes it very important to dispose of your ThreadLocal instances if you'll be using lots of them, so the type instantiations can be recycled. The previous way of creating arbitary thread-static variables, thread data slots, was slow, clunky, and hard to use. In comparison, ThreadLocal can be used just like any other type, and each instance appears from the outside to be a non-static thread-static variable. It does this by using the CLR type system to assign each instance of ThreadLocal its own instantiated type containing a thread-static field, and so delegating a lot of the bookkeeping that thread data slots had to do to the CLR type system itself! That's a very clever use of the CLR type system.

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