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• Interchange structured data between Haskell and C

  - by Eonil

  First, I'm a Haskell beginner. I'm planning integrating Haskell into C for realtime game. Haskell does logic, C does rendering. To do this, I have to pass huge complexly structured data (game state) from/to each other for each tick (at least 30 times per second). So the passing data should be lightweight. This state data may laid on sequential space on memory. Both of Haskell and C parts should access every area of the states freely. In best case, the cost of passing data can be copying a pointer to a memory. In worst case, copying whole data with conversion. I'm reading Haskell's FFI(http://www.haskell.org/haskellwiki/FFICookBook#Working_with_structs) The Haskell code look specifying memory layout explicitly. I have a few questions. Can Haskell specify memory layout explicitly? (to be matched exactly with C struct) Is this real memory layout? Or any kind of conversion required? (performance penalty) If Q#2 is true, Any performance penalty when the memory layout specified explicitly? What's the syntax #{alignment foo}? Where can I find the document about this? If I want to pass huge data with best performance, how should I do that? *PS Explicit memory layout feature which I said is just C#'s [StructLayout] attribute. Which is specifying in-memory position and size explicitly. http://www.developerfusion.com/article/84519/mastering-structs-in-c/ I'm not sure Haskell has matching linguistic construct matching with fields of C struct.

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• Windows Phone and Silverlight ListBox.ItemTemplate

  - by user551308

  Hi, I have a Windows Phone 7 application with the following listbox and every item contains 2 textblocks and a HyperlinkButton. <ListBox.ItemTemplate> In the ViewModel constructor I have the following code: GetCommand = new RelayCommand(() ={some code}); where GetCommand is a property : public RelayCommand GetCommand { get; private set; } My problem is that GetCommand = new RelayCommand(() ={some code}); is not executing when I press the button. I must say that if dont place the HyperlinkButton insise the itemTemplate, everything works fine. I use the Galasoft mvvm light tookit - http://www.galasoft.ch/mvvm/getstarted/ I appreciate any help.

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• Using a delegate to populate a listbox

  - by Leroy Jenkins

  Ive been playing around with delegates trying to learn and I ran into one small problem Im hoping you can help me with. class myClass { OtherClass otherClass = new OtherClass(); // Needs Parameter otherClass.SendSomeText(myString); } class OtherClass { public delegate void TextToBox(string s); TextToBox textToBox; public OtherClass(TextToBox ttb) // ***Problem*** { textToBox = ttb; } public void SendSomeText(string foo) { textToBox(foo); } } the form: public partial class MainForm : Form { OtherClass otherClass; public MainForm() { InitializeComponent(); otherClass = new OtherClass(this.TextToBox); } public void TextToBox(string aString) { listBox1.Items.Add(aString); } } Obviously this doesnt compile because the OtherClass constructor is looking for TextToBox as a parameter. How would you recommend getting around the issue so I can get an object from myClass into the textbox in the form?

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• Android: Send arbitrary objects within Activities?

  - by Sebastian

  I have read some question here but I didn't find a solution. I have read about Parcelable, Intents, and sharing specific data within Activities from the android dev docs (both dev guide and reference). Here's the scenario: I have one ListActivity that fills in an object parsing an xml file, it shows a list of values, and when clicked I want to return the object that represents the item clicked to the activity that has called it, for then, call another activity with this object. I read on how to implement Parcelable but seems not being the way. Implementing Parcelable receives a Parcel for the constructor and then reads the values from it (or at least that was what I understood). This makes no sense for me and I can't see how to implement basing on that issue. I build the object parsing the xml file, not having a Parcel. I appreciate some clarifications on this, regards.

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• c# ref keyword... Am i passing my value correctly?

  - by Pandiya Chendur

  Is this a valid value for this c# class default constructor, public class SMSCOMMS { public SMSCOMMS(ref string COMMPORT) { SMSPort = new SerialPort(); SMSPort.PortName = COMMPORT; SMSPort.BaudRate = 9600; SMSPort.Parity = Parity.None; SMSPort.DataBits = 8; SMSPort.StopBits = StopBits.One; SMSPort.Handshake = Handshake.RequestToSend; SMSPort.DtrEnable = true; SMSPort.RtsEnable = true; SMSPort.NewLine = System.Environment.NewLine; ReadThread = new Thread( new System.Threading.ThreadStart(ReadPort)); } and i am passing this value, SMSCOMMS SMSEngine = new SMSCOMMS("COM6"); but it doesn't seem to take "COM6" as a valid ref string... Any suggestion..

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• Does the "Supporting Multiple Screens" document contradict itself?

  - by Neil Traft

  In the Supporting Multiple Screens document in the Android Dev Guide, some example screen configurations are given. One of them states that the small-ldpi designation is given to QVGA (240x320) screens with a physical size of 2.6"-3.0". According to this DPI calculator, a 2.8" QVGA display equates to 143 dpi. However, further down the page the document explicitly states that all screens over 140 dpi are considered "medium" density. So which is it, ldpi or mdpi? Is this a mistake? Does anyone know what the HTC Tattoo or similar device actually reports? I don't have access to any devices like this. Also, with the recent publishing of this document, I'm glad to see we finally have an explicit statement of the exact DPI ranges of the three density categories. But why haven't we been given the same for the small, medium, and large screen size categories? I'd like to know the exact ranges for all these. Thanks in advance for your help!

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• How can I access and change elements in this private readonly property?

  - by CrimsonX

  I'm trying to figure out how I am able to successfully change a "readonly" array. I have this: namespace ConsoleApplication1 { class Program { static void Main(string[] args) { MyClass myClass = new MyClass(); myClass.Time[5] = 5; // How is this legal? } } public class MyClass { private readonly uint[] time; public IList<uint> Time { get { return time; } } public MyClass() { time = new uint[7]; } } } As I Note above, I would expect that Time[5] would be illegal due to the fact that public IList Time does not have a setter. Additionally, how can I create an array in the constructor which is read-only and unchangeable outside of this class?

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• Overriding constructors

  - by demas

  Here is sample code: class One def initialize(*args) case args.size when 0 puts "one initialize" when 1 puts "one initialize #{args[0]}" end end end class Two def initialize(*args) if args.size == 2 then puts "two initialize #{args[0]} and #{args[1]}" else super(args) end end end one = One.new one = One.new("thing") two = Two.new("some", "other") two = Two.new("some") Now I'm launching the code and getting the error message: [[email protected]][~/temp]% ruby test2.rb one initialize one initialize thing two initialize some and other test2.rb:17:in `initialize': wrong number of arguments(1 for 0) (ArgumentError) from test2.rb:17:in `initialize' from test2.rb:26:in `new' from test2.rb:26:in `<main>' How can I call parent's constructor from class Two ?

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• What is the proper way to access datastore in custom Model Binders?

  - by mare

  How should I properly implement data access in my custom model binders? Like in controllers I use IContentRepository and then have it create an instance of its implementing class in constructor. So I have everything ready for incorporating IoC (DI) at a later stage. Now I need something similar in model binder. I need to make some DB lookups in the binder. I'm thinking of doing it the same way I do it in controllers but I am open to suggestion. This is a snippet from one of my controllers so you can imagine how I'm doing it in them: public class WidgetZoneController : BaseController { // BaseController has IContentRepository ContentRepository field public WidgetZoneController() : this(new XmlWidgetZoneRepository()) { } public WidgetZoneController(IContentRepository repository) { ContentRepository = repository; } ...

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• Lua metatable Objects cannot be purge from memory?

  - by Prometheus3k

  Hi there, I'm using a proprietary platform that reported memory usage in realtime on screen. I decided to use a Class.lua I found on http://lua-users.org/wiki/SimpleLuaClasses However, I noticed memory issues when purging object created by this using a simple Account class. Specifically, I would start with say 146k of memory used, create 1000 objects of a class that just holds an integer instance variable and store each object into a table. The memory used is now 300k I would then exit, iterating through the table and setting each element in the table to nil. But would never get back the 146k, usually after this I am left using 210k or something similar. If I run the load sequence again during the same session, it does not exceed 300k so it is not a memory leak. I have tried creating 1000 integers in a table and setting these to nil, which does give me back 146k. In addition I've tried a simpler class file (Account2.lua) that doesn't rely on a class.lua. This still incurs memory fragmentation but not as much as the one that uses Class.lua Can anybody explain what is going on here? How can I purge these objects and get back the memory? here is the code --------Class.lua------ -- class.lua -- Compatible with Lua 5.1 (not 5.0). --http://lua-users.org/wiki/SimpleLuaClasses function class(base,ctor) local c = {} -- a new class instance if not ctor and type(base) == 'function' then ctor = base base = nil elseif type(base) == 'table' then -- our new class is a shallow copy of the base class! for i,v in pairs(base) do c[i] = v end c._base = base end -- the class will be the metatable for all its objects, -- and they will look up their methods in it. c.__index = c -- expose a ctor which can be called by () local mt = {} mt.__call = function(class_tbl,...) local obj = {} setmetatable(obj,c) if ctor then ctor(obj,...) else -- make sure that any stuff from the base class is initialized! if base and base.init then base.init(obj,...) end end return obj end c.init = ctor c.instanceOf = function(self,klass) local m = getmetatable(self) while m do if m == klass then return true end m = m._base end return false end setmetatable(c,mt) return c end --------Account.lua------ --Import Class template require 'class' local classname = "Account" --Declare class Constructor Account = class(function(acc,balance) --Instance variables declared here. if(balance ~= nil)then acc.balance = balance else --default value acc.balance = 2097 end acc.classname = classname end) --------Account2.lua------ local account2 = {} account2.classname = "unnamed" account2.balance = 2097 -----------Constructor 1 do local metatable = { __index = account2; } function Account2() return setmetatable({}, metatable); end end --------Main.lua------ require 'Account' require 'Account2' MAX_OBJ = 5000; test_value = 1000; Obj_Table = {}; MODE_ACC0 = 0 --integers MODE_ACC1 = 1 --Account MODE_ACC2 = 2 --Account2 TEST_MODE = MODE_ACC0; Lua_mem = ""; print("##1) collectgarbage('count'): " .. collectgarbage('count')); function Load() for i=1, MAX_OBJ do if(TEST_MODE == MODE_ACC0 )then table.insert(Obj_Table, test_value); elseif(TEST_MODE == MODE_ACC1 )then table.insert(Obj_Table, Account(test_value)); --Account.lua elseif(TEST_MODE == MODE_ACC2 )then table.insert(Obj_Table, Account2()); --Account2.lua Obj_Table[i].balance = test_value; end end print("##2) collectgarbage('count'): " .. collectgarbage('count')); end function Purge() --metatable purge if(TEST_MODE ~= MODE_ACC0)then --purge stage 0: print("set each elements metatable to nil") for i=1, MAX_OBJ do setmetatable(Obj_Table[i], nil); end end --purge stage 1: print("set table element to nil") for i=1, MAX_OBJ do Obj_Table[i] = nil; end --purge stage 2: print("start table.remove..."); for i=1, MAX_OBJ do table.remove(Obj_Table, i); end print("...end table.remove"); --purge stage 3: print("create new object_table {}"); Obj_Table= {}; --purge stage 4: print("collectgarbage('collect')"); collectgarbage('collect'); print("##3) collectgarbage('count'): " .. collectgarbage('count')); end --Loop callback function OnUpdate() collectgarbage('collect'); Lua_mem = collectgarbage('count'); end ------------------- --NOTE: --On start of game runs Load(), another runs Purge() --Update I've updated the code with suggestions from comments below, and will post my findings later today.

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• Perfect hash in Scala.

  - by Lukasz Lew

  I have some class C: class C (...) { ... } I want to use it to index an efficient map. The most efficient map is an Array. So I add a "global" "static" counter in companion object to give each object unique id: object C { var id_counter = 0 } In primary constructor of C, with each creation of C I want to remember global counter value and increase it. Question 1: How to do it? Now I can use id in C objects as perfect hash to index array. But array does not preserve type information like map would, that a given array is indexed by C's id. Question 2: Is it possible to have it with type safety?

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• page redirection problem via Bean in Js1.1

  - by johnbritto

  I have a requested scoped managed bean, called AuthenticationBean. I am developing a smal application with a login module, user activation and deactivation. When I click on the activate or deactivate link, then the action is processed in AuthenticationBean. I want thereafter redirect to some page depending on the activate or deactivate link. I have tried the following in the bean constructor: FacesContext.getCurrentInstance().getExternalContext().redirect("/user/activate.jsp"); But this code is not working. Please help me.

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• Why can I call a non-const member function pointer from a const method?

  - by sdg

  A co-worker asked about some code like this that originally had templates in it. I have removed the templates, but the core question remains: why does this compile OK? #include <iostream> class X { public: void foo() { std::cout << "Here\n"; } }; typedef void (X::*XFUNC)() ; class CX { public: explicit CX(X& t, XFUNC xF) : object(t), F(xF) {} void execute() const { (object.*F)(); } private: X& object; XFUNC F; }; int main(int argc, char* argv[]) { X x; const CX cx(x,&X::foo); cx.execute(); return 0; } Given that CX is a const object, and its member function execute is const, therefore inside CX::execute the this pointer is const. But I am able to call a non-const member function through a member function pointer. Are member function pointers a documented hole in the const-ness of the world? What (presumably obvious to others) issue have we missed?

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• Passing an array for setting variable

  - by mathk

  Hi, I often see this idiom when reading php code: public function __construct($config) { if (array_key_exists('options', $config)) { ... } if (array_key_exists('driver_options', $config)) { ... } } Here I am concern with the way the parameter is used. If I were in lisp I would do: (defun ct (&key options driver_options) (do-something-with-option-and-driver_option)) But since I am in PHP I would rather have a constructor that take a list of parameter and let them be null if there a not require. So what do you guys think about having an array as parameter in other to do some initialization-or-whatever? In other to answer you have to take in account the point of view of the user of the function and the designer of the API. Also have you ever heard this has a code-smell? thanks

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• Problems with delete in destructor

  - by Vera

  Hello, I wrote this code. The constructor works normally, but in the destructor I get "Windows has triggered a breakpoint." How should I correct this? template class CyclicalArray { private: T* mem_ptr; public: CyclicalArray(size_t capacity, const T& default_value) { this->default_value = default_value; this->capacity = capacity; head_index = 0; mem_ptr = ::new T[capacity]; //memory allocating for(T* p = mem_ptr; p < mem_ptr + capacity * sizeof(T); p += sizeof(T)) { ::new (p) T (default_value); //initialization } } ~CyclicalArray() { for(T* p = mem_ptr + sizeof(T); p < mem_ptr + capacity * sizeof(T); p += sizeof(T)) { p->~T(); } delete[] mem_ptr; }

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• Where to maintain common information, that could be accessed by all forms

  - by The King

  Hi All, This is my first winform app in .NET... I have made a couple of ASP.NET app... In this app, I have some common variables, like current user name, his selected process etc.. etc.. This should be made accessible from all forms in the app at any time... How could I do this... Is there any place like "Session" in ASP.NET here... Further How do coders generally pass information from one form to another... Here I want to pass on the info I acquired in the first form to the subsequent forms... I use constructor overloading and pass the values as parameters... I'm pretty sure there has to be a better way to do it... Thanks for your time...

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• Code in Global.asax prevents webpage from loading

  - by pete the pagan-gerbil

  I've made a static class to hold a number of configuration values (and also swap these values out in unit tests). If I initialise it in the Global.asax, the code runs correctly but the page doesn't load at all, and trying to navigate to a specific page fails. I can't initialise the values in a constructor or inline on the field declarations, because I need to be able to swap the values out in unit tests before the web.config is interrogated. Basically, putting the one line "ConfigClass.SetValues()" in the Global.asax prevents the app from loading correctly (although, as I say, it runs the code fine) and removing it again makes the app load properly - but without the class values initialised. As an aside, I'm sure I had this working correctly and being initialised in the Global.asax yesterday. I'm positive I didn't take any action to change or break it... Does anyone have advice on how I might track down what's going on here? Was I mistaken that it worked before (always possible) and that I need to go back and redesign something?

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• Create custom component based on LinearLayout, declaring layout in XML

  - by pheelicks

  I've been trying to create a Compound Control in Android 1.5 (as described here) but havn't been able to find any good examples on how to do this using an XML file to specify a layout. I'm fine with creating an Activity and then loading an xml file using the following in the constructor: setContentView(R.layout.main); However, I want to do this in subclass of LinearLayout - so I can use this compound component in other XML layouts. Something along the lines of: public class CustomView extends LinearLayout { public CustomView(Context context) { super(context); setupView(); } public CustomView(Context context, AttributeSet attrs) { super(context, attrs); setupView(); } public void setupView() { setContentView(R.layout.custom); // Not possible } } What is the correct way of going about doing this?

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• How can I pass methods in javascript?

  - by peterjwest

  I often need to pass methods from objects into other objects. However I usually want the method to be attached to the original object (by attached I mean 'this' should refer to the original object). I know a few ways to do this: a) In the object constructor: ObjectA = function() { var that = this; var method = function(a,b,c) { that.abc = a+b+c }} b) In objectA which has been passed objectB: objectB.assign(function(a,b,c) { that.method(a,b,c) }) c) Outside both objects: objectB.assign(function(a,b,c) { objectA.method(a,b,c) }) I want to know if there is a simpler way to pass methods attached to their original objects.

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• StructureMap - Injecting a dependency into a base class?

  - by David

  In my domain I have a handful of "processor" classes which hold the bulk of the business logic. Using StructureMap with default conventions, I inject repositories into those classes for their various IO (databases, file system, etc.). For example: public interface IHelloWorldProcessor { string HelloWorld(); } public class HelloWorldProcessor : IHelloWorldProcessor { private IDBRepository _dbRepository; public HelloWorldProcessor(IDBRepository dbRepository) { _dbRepository = dbrepository; } public string HelloWorld(){ return _dbRepository.GetHelloWorld(); } } Now, there are some repositories that I'd like to be available to all processors, so I made a base class like this: public class BaseProcessor { protected ICommonRepository _commonRepository; public BaseProcessor(ICommonRepository commonRepository) { _commonRepository = commonRepository; } } But when my other processors inherit from it, I get a compiler error on each one saying that there's no constructor for BaseProcessor which takes zero arguments. Is there a way to do what I'm trying to do here? That is, to have common dependencies injected into a base class that my other classes can use without having to write the injections into each one?

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• extension method phone format with country code as parameter

  - by frenchie

  Hi, I'm writing an extension method called ToPhoneFormat that formats a string of digits to phone numbers. Is it possible to add a parameter to the method that would enable me to call it like this: MyPhoneString.ToPhoneFormat(international code) That way, I could write MyPhoneString.ToPhoneFormat(1); to format a US phone number and MyPhoneString.ToPhoneFormat(33) to format a French phone number. I already wrote the method that does the formatting but I'm wondering how to build the constructor so that it works with a parameter when I'm calling it. Thanks.

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• c#, Internal, and Reflection

  - by cyberconte

  Duplicate of: Accessing internal members via System.Reflection? Is there a way to execute "internal" code via reflection? Here is an example program: using System; using System.Reflection; namespace ReflectionInternalTest { class Program { static void Main(string[] args) { Assembly asm = Assembly.GetExecutingAssembly(); // Call normally new TestClass(); // Call with Reflection asm.CreateInstance("ReflectionInternalTest.TestClass", false, BindingFlags.Default | BindingFlags.CreateInstance, null, null, null, null); // Pause Console.ReadLine(); } } class TestClass { internal TestClass() { Console.WriteLine("Test class instantiated"); } } } Creating a testclass normally works perfectly, however when i try to create an instance via reflection, I get a missingMethodException error saying it can't find the Constructor (which is what would happen if you tried calling it from outside the assembly). Is this impossible, or is there some workaround i can do?

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• alternative to #include within namespace { } block

  - by Jeff

  Edit: I know that method 1 is essentially invalid and will probably use method 2, but I'm looking for the best hack or a better solution to mitigate rampant, mutable namespace proliferation. I have multiple class or method definitions in one namespace that have different dependencies, and would like to use the fewest namespace blocks or explicit scopings possible but while grouping #include directives with the definitions that require them as best as possible. I've never seen any indication that any preprocessor could be told to exclude namespace {} scoping from #include contents, but I'm here to ask if something similar to this is possible: (see bottom for explanation of why I want something dead simple) // NOTE: apple.h, etc., contents are *NOT* intended to be in namespace Foo! // would prefer something most this: namespace Foo { #include "apple.h" B *A::blah(B const *x) { /* ... */ } #include "banana.h" int B::whatever(C const &var) { /* ... */ } #include "blueberry.h" void B::something() { /* ... */ } } // namespace Foo ... // over this: #include "apple.h" #include "banana.h" #include "blueberry.h" namespace Foo { B *A::blah(B const *x) { /* ... */ } int B::whatever(C const &var) { /* ... */ } void B::something() { /* ... */ } } // namespace Foo ... // or over this: #include "apple.h" namespace Foo { B *A::blah(B const *x) { /* ... */ } } // namespace Foo #include "banana.h" namespace Foo { int B::whatever(C const &var) { /* ... */ } } // namespace Foo #include "blueberry.h" namespace Foo { void B::something() { /* ... */ } } // namespace Foo My real problem is that I have projects where a module may need to be branched but have coexisting components from the branches in the same program. I have classes like FooA, etc., that I've called Foo::A in the hopes being able to branch less painfully as Foo::v1_2::A, where some program may need both a Foo::A and a Foo::v1_2::A. I'd like "Foo" or "Foo::v1_2" to show up only really once per file, as a single namespace block, if possible. Moreover, I tend to prefer to locate blocks of #include directives immediately above the first definition in the file that requires them. What's my best choice, or alternatively, what should I be doing instead of hijacking the namespaces?

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• Why is partial specialziation of a nested class template allowed, while complete isn't?

  - by drhirsch

  template<int x> struct A { template<int y> struct B {};. template<int y, int unused> struct C {}; }; template<int x> template<> struct A<x>::B<x> {}; // error: enclosing class templates are not explicitly specialized template<int x> template<int unused> struct A<x>::C<x, unused> {}; // ok So why is the explicit specialization of a inner, nested class (or function) not allowed, if the outer class isn't specialiced too? Strange enough, I can work around this behaviour if I only partially specialize the inner class with simply adding a dummy template parameter. Makes things uglier and more complex, but it works. Note: I need this feature for recursive templates of the inner class for a set of the outer class. To make things even more complicate, in reality I only need a template function instead of the inner class. But partial specialization of functions is generally disallowed somewhere else in the standard ^^

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• C++ interface inheritance problem

  - by james t

  Hey, i'm trying to create a c++ stomp client, my client constructor is : Client(std::string &server, short port, std::string &login, std::string &pass, Listener &listener); it gets a listener object which when Listener is the following interface : class Listener { virtual void message(StmpMessage message) =0; }; now i attempt to instantiate a client in a test class : class test : public virtual Listener { public: void message(StmpMessage message) { message.prettyPrint(); } int main(int argc, char* argv[]) { Client client("127.0.0.1", 61613, *this); return 0; } }; i'm sending this to the client because this is a listener object, i get the following error : /Users/mzruya/Documents/STOMPCPP/main.cpp:18: error: no matching function for call to 'Client::Client(const char [10], int, test&)' /Users/mzruya/Documents/STOMPCPP/Client.h:43: note: candidates are: Client::Client(std::string&, short int, std::string&, std::string&, Listener&) /Users/mzruya/Documents/STOMPCPP/Client.h:37: note: Client::Client(const Client&)

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