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• JLS: Item 54 - Why classes having thread pool should not implement serializable?

  - by Maddy

  From what I understand, the object state is just stored (values for fields, etc.), however, the execution context is anyways going to be lost. What's the point of this? What bad can happen if so? Note* this was taken from Effective Java By Joshua Bloch

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• Is it good practice to generally make heavyweight classes non-copyable?

  - by Emile Cormier

  I have a Shape class containing potentially many vertices, and I was contemplating making copy-constructor/copy-assignment private to prevent accidental needless copying of my heavyweight class (for example, passing by value instead of by reference). To make a copy of Shape, one would have to deliberately call a "clone" or "duplicate" method. Is this good practice? I wonder why STL containers don't use this approach, as I rarely want to pass them by value.

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• What's the best way to validate EntityFramwork 4.0 classes?

  - by lsb

  Hi! I've done a fair amount of searching but I've yet to find an easy way to validate EntityFramework 4.0 entities passed accross the wire via WCF Data Services. Basically, I want to do something on the client like: Proxy.MyEntities entities = new Proxy.MyEntities( new Uri("http://localhost:2679/Service.svc")); Proxy.Vendor vendor = new Proxy.Vendor(); vendor.Code = "ABC/XYZ"; vendor.Status = "ACTIVE"; // I'd like to do something like the following: vendor.Validate(); entities.AddToVendors(vendor); entities.SaveChanges(); Any help in this regard would be greatly appreciated!

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• Can LINQ expression classes implement the observer pattern instead of deferred execution?

  - by Tormod

  Hi. We have issues within an application using a state machine. The application is implemented as a windows service and is iteration based (it "foreaches" itself through everything) and there are myriads of instances being processed by the state machine. As I'm reading the MEAP version of Jon Skeets book "C# in Depth, 2nd ed", I'm wondering if I can change the whole thing to use linq expression instances so that guards and conditions are represented using expression trees. We are building many applications on this state machine engine and would probably greatly benefit from the new Expression tree visualizer in VS 2010 Now, simple example. If I have an expression tree where there is an OR Expression condition with two sub nodes, is there any way that these can implement the observer pattern so that the expression tree becomes event driven? If a condition change, it should notify its parent node (the OR node). Since the OR node then changes from "false" to "true", then it should notify ITS parent and so on. I love the declarative model of expression trees, but the deferred execution model works in opposite direction of the control flow if you want event based "live" conditions. Am I off on a wild goose chase here? Or is there some concept in the BCL that may help me achieve this?

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• Why can't you call abstract functions from abstract classes in PHP?

  - by incrediman

  I've set up an abstract parent class, and a concrete class which extends it. Why can the parent class not call the abstract function? //foo.php <?php abstract class AbstractFoo{ abstract public static function foo(); public static function getFoo(){ return self::foo();//line 5 } } class ConcreteFoo extends AbstractFoo{ public static function foo(){ return "bar"; } } echo ConcreteFoo::getFoo(); ?> Error: Fatal error: Cannot call abstract method AbstractFoo::foo() in foo.php on line 5

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• How can I dynamically override a classes "each" method?

  - by rewbs

  Groovy adds each() and a number of other methods to java.lang.Object. I can't figure out how to use the Groovy metaclass to dynamically replace the default each() on a Java class. I can see how to add new methods: MyJavaClass.metaClass.myNewMethod = { closure -> /* custom logic */ } new MyJavaClass().myNewMethod { item -> println item } // runs custom logic But it seems the same approach doesn't work when overriding methods: MyJavaClass.metaClass.each = { closure -> /* custom logic */ } new MyJavaClass().each { item -> println item } // runs Object.each() What am I doing wrong? How can I dynamically override each() in Groovy?

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• Differentiate generic methods by type parameters only using reflection?

  - by Brian Vallelunga

  I'm trying to use reflection to get a specific MethodInfo of a class, but am unsure how to differentiate between the two following methods: public class Test { public IBar<T1> Foo<T1>(); public IBar<T1, T2> Foo<T1, T2>(); } How can I get a reference to the different Foo methods, assuming I know the number of type parameters? Just calling typeof(Test).GetMethod("Foo") will throw an exception that the method name is ambiguous and there aren't a differing number of parameters to check.

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• Why isn't DBIx::Class::Schema::Loader creating my classes?

  - by Robert Wohlfarth

  I am trying to generate static schemas using DBIx::Class in Perl. The command shown below outputs a Schema.pm and no other files. Any idea what I'm doing wrong, or how to to debug this? U:\wohlfarj\Software\PARS>perl -MDBIx::Class::Schema::Loader=make_schema_at,dump_to_dir:.\lib -e "make_schema_at('PARS::Schema',{debug=>1},['dbi:ODBC:PARS','user','password',{AutoCommit=>0}])" Dumping manual schema for PARS::Schema to directory .\lib ... Schema dump completed. I'm using Strawberry Perl on Windows XP. The database is SQL Server 2000, accessed through an ODBC connection. I can successfully run queries using plain old DBI with the same ODBC connection.

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• Why would this line throw exception for type initializer failed?

  - by Jaggu

  I had a class: public class Constant { public static string ConnString = ConfigurationManager.ConnectionStrings["ConnString"].ConnectionString; } which would throw exception on LIVE: Type initialize failed for Constant ctor If I change the class to: public class Constant { public static string ConnString { get { return ConfigurationManager.ConnectionStrings["ConnString"].ConnectionString; } } } it works. I wasted 2 hours behind this but I still don't know why would this happen. Any ideas? Note: The 1st class used to work on DEV environment but not on LIVE. The 2nd class works on DEV and also on Production. I am using VS2010 on production and Asp.Net 4.0 Website project. I am totally amazed by this inconsistency to say the least! Edit: This class was in App_Code folder.

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• Strategy game programming in Java, how the map and unit classes should work/relate each other.

  - by Gabriel A. Zorrilla

  As a way of learning Java i'm doing a little strategy game. You have a game map and military units. The gamemap and the units are Jpanels which are binded together in another class called GameWindow, which has a JLayeredPane where the gamepap is below the units. Every time i click a unit (and therefore, the JPane) I can get the unit's information. The problem comes when i want to move a unit... each unit is self drawn inside it's Jpanel, how do i represent the change in position over the gamemap? I'm thinking about reloading the whole game window based on a position change of a unit (because the JPAnels that represent the units are created in the GameWindow, not drawn in the gamemap). Another more elegant option, should be repainting the whole map, with the units. But that way the units would lose it's status of objects (no more JPAnels, just being drawn in the gamemap paint() method), and how would i tell if one unit is clicked? I dont know how people with more experience in games handle the class structure in strategy games. I believe i have the right structure (map, game units, each one an object) but I'm having difficulties making it work together. Here is a snapshot of the map with a couple of units:

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• Declaring pointers; asterisk on the left or right of the space between the type and name?

  - by GenTiradentes

  I've seen mixed versions of this in a lot of code. (This applies to C and C++, by the way.) People seem to declare pointers in one of two ways, and I have no idea which one is correct, of if it even matters. The first way it to put the asterisk adjacent the type name, like so: someType* somePtr; The second way is to put the asterisk adjacent the name of the variable, like so: someType *somePtr; This has been driving me nuts for some time now. Is there any standard way of declaring pointers? Does it even matter how pointers are declared? I've used both declarations before, and I know that the compiler doesn't care which way it is. However, the fact that I've seen pointers declared in two different ways leads me to believe that there's a reason behind it. I'm curious if either method is more readable or logical in some way that I'm missing.

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• C++: warning: '...' declared with greater visibility than the type of its field '...::<anonymous>'

  - by Albert

  I'm getting these two warnings (with GCC 4.2 on MacOSX): /Users/az/Programmierung/openlierox/build/Xcode/../../src/main.cpp:154:0 /Users/az/Programmierung/openlierox/build/Xcode/../../src/main.cpp:154: warning: 'startMainLockDetector()::MainLockDetector' declared with greater visibility than the type of its field 'startMainLockDetector()::MainLockDetector::<anonymous' /Users/az/Programmierung/openlierox/build/Xcode/../../src/main.cpp:154:0 /Users/az/Programmierung/openlierox/build/Xcode/../../src/main.cpp:154: warning: 'startMainLockDetector()::MainLockDetector' declared with greater visibility than its base 'Action' In this code: struct Action { virtual ~Action() {} virtual int handle() = 0; }; static void startMainLockDetector() { /* ... */ struct MainLockDetector : Action { bool wait(Uint32 time) { /* ... */ } int handle() { /* ... */ } }; /* ... */ } I'm not exactly sure what these warnings mean (what visibility?) and how to fix them. (I really want the class MainLockDetector to be local for that function only.) I have already compiled the same code with a lot of other compilers (clang, GCC 3.*, GCC 4.0, GCC 4.4, etc) and never got any warning for this code.

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• What databse uses these specific type of .dat and .idx files?

  - by Cape Cod Gunny

  I'm trying to figure out what type of database uses these specific .dat and .idx files. When I view the .dat files using a binary file reader I see Record Schema followed by somewhat decipherable data names. A little further down I see Key Schema whch apears to be a comma separated list of clear text references. Each .dat file has a matching .idx file. Each .dat file contains the phrase "Record Schema" and "Key Schema" as described above. How would I convert these files so I can use them in an SQL database?

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• Why does Perl's shift complain 'Type of arg 1 to shift must be array (not grep iterator).'?

  - by wes

  I've got a data structure that is a hash that contains an array of hashes. I'd like to reach in there and pull out the first hash that matches a value I'm looking for. I tried this: my $result = shift grep {$_->{name} eq 'foo'} @{$hash_ref->{list}}; But that gives me this error: Type of arg 1 to shift must be array (not grep iterator). I've re-read the perldoc for grep and I think what I'm doing makes sense. grep returns a list, right? Is it in the wrong context? I'll use a temporary variable for now, but I'd like to figure out why this doesn't work.

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• In ActionScript, Is there a way to check if an input argument is a valid Vector of any type?

  - by ty

  In the following code: var a:Vector.<int> ... var b:Vector.<String> ... var c:Vector.<uint> ... var c:Vector.<MyOwnClass> ... function verifyArrayLike(arr:*):Boolean { return (arr is Array || arr is Vector) } verifyArrayLike(a); verifyArrayLike(b); ... What I'm looking for is something like _var is Vector.<*> But Vector.<*> is not a valid expression, even Vector. can not be placed at the right side of operators. Is there a way to check if an input argument is a valid Vector of any type?

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• Is there a design pattern for injecting methods into a class?

  - by glenn I.

  I have a set of classes that work together (I'm coding in javascript). There is one parent class and a number of child classes that are instantiated by the parent class. I have a number of clients of these classes that each need to add on one more methods to the parent or child classes. Rather than having each client inherit from these classes, which is doable but messy because of the child classes, I am having these clients pass functions into the parent class when they instantiate the main class. The main class creates the methods dynamically and the clients can call the methods like they were there all along. My questions are: is this a sensible thing to do? what would the design pattern be for what I am doing?

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• How do I integrate GUI elements from different classes at runtime?

  - by thefourthdoctor

  I'm trying to "future-proof" an application that I'm writing by splitting out those elements that are likely to change over time. In my application I need to be able to adapt to changes in the output format (e.g. today I output to a CSV file, in the future I may need to output directly to a SQL Server database, or to a web service, etc.). I'm handling this by defining an abstract class ("OutputProvider") that I will subclass for each individual case. The one aspect of this that has me stumped is how to provide a configuration GUI that is specific to each concrete class. I have a settings dialog with a tab for output configuration. On that tab I intend to provide a drop-down to select the provider and a JPanel beneath it to hold the contents of the provider-specific GUI. How do I get the right GUI in that panel at runtime and have it behave correctly with respect to events? Also, a bonus would be if there was a way to do this such that in order to add support for new providers I could simply provide a new jar or class file to be dropped in a specific folder and the application could pick that up at startup. I'm using NetBeans and Swing.

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• Classes with the same name - is it restricted only within the same translation unit?

  - by LeopardSkinPillBoxHat

  Let's just I had the following code: foo.h class Foo { // ... }; foo.cpp #include "foo.h" // Functions for class Foo defined here... Let's say that Foo are built into a static library foo.lib. Now let's say I have the following: foo2.h class Foo { // ... }; foo2.cpp #include "foo2.h" // Functions for class Foo defined here... This is built into a separate static library foo2.lib. Now, if I re-link foo.lib and foo2.lib into an executable program foo.exe, should it be complaining that class Foo has been defined twice? In my experiences, neither the compiler or the linker are complaining. I wouldn't be expecting the compiler to complain, because they have been defined in separate translation units. But why doesn't the linker complain? How does the linker differentiate between the 2 versions of the Foo class? Does it work by decorating the symbols?

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• Can I use foreach to return only a certain type from a collection?

  - by RoboShop

  If I enter the code below, I get an error. Basically, the foreach will break when it comes across a Control that isn't a label. foreach (Label currControl in this.Controls()) { ... } I have to do something like this. foreach (Control currControl in this.Controls()) { if(typeof(Label).Equals(currControl.GetType())){ ... } } can anyone think of a better way of doing it without me needing to check the type? Can I somehow get foreach to skip the objects that aren't Labels?

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• Is there a module that implements an efficient array type in Erlang?

  - by dsmith

  I have been looking for an array type with the following characteristics in Erlang. append(vector(), term()) O(1) nth(Idx, vector()) O(1) set(Idx, vector(), term()) O(1) insert(Idx, vector(), term()) O(N) remove(Idx, vector()) O(N) I normally use a tuple for this purpose, but the performance characteristics are not what I would want for large N. My testing shows the following performance characteristics... erlang:append_element/2 O(N). erlang:setelement/3 O(N). I have started on a module based on the clojure.lang.PersistentVector implementation, but if it's already been done I won't reinvent the wheel.

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• For what purpose does java have a float primitive type?

  - by Roman

  I heard plenty times different claims about float type in java. The most popular issues typicaly regard to converting float value to double and vice versa. I read (rather long time ago and not sure that it's actual now with new JVM) that float gives much worse performance then double. And it's also not recommended to use float in scientific applications which should have certain accuracy. I also remember that when I worked with AWT and Swing I had some problems with using float or double (like using Point2D.Float or Point2D.Double). So, I see only 2 advantages of float over double: it needs only 4 bytes while double needs 8 bytes JMM garantees that assignment operation is atomic with float variables while it's not atomic with double's. Are there any other cases where float is better then double? Do you use float's in your applications? It seems to me that the only valuable reason java has float is backward compatibility.

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• What data type should I use for my texture coordinates in OpenGL ES?

  - by Matthew Chen

  I notice that the default data type for texture coordinates in the OpenGL docs is GLfloat, but much of the sample code I see written by experienced iphone developers uses GLshort or GLbyte. Is this an optimization? GLfloat vertices[] = { // Upper left x1, y2, // Lower left x1, y1, // Lower right x2, y1, // Upper right x2, y2, }; glTexCoordPointer(2, GL_FLOAT, 0, iconSTs); vs. GLbyte vertices[] = { // Upper left x1, y2, // Lower left x1, y1, // Lower right x2, y1, // Upper right x2, y2, }; glTexCoordPointer(2, GL_BYTE, 0, iconSTs);

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• What is the proper way to declare a specialization of a template for another template type?

  - by Head Geek

  The usual definition for a specialization of a template function is something like this: class Foo { [...] }; namespace std { template<> void swap(Foo& left, Foo& right) { [...] } } // namespace std But how do you properly define the specialization when the type it's specialized on is itself a template? Here's what I've got: template <size_t Bits> class fixed { [...] }; namespace std { template<size_t Bits> void swap(fixed<Bits>& left, fixed<Bits>& right) { [...] } } // namespace std Is this the right way to declare swap? It's supposed to be a specialization of the template function std::swap, but I can't tell whether the compiler is seeing it as such, or whether it thinks that it's an overload of it or something.

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• how do i use MySql ENUM type? (and is it right for a news feed)

  - by Haroldo

  I'm creating a table called news_feed, this will log all the actions a user performs. Lets say I want to store user1234 deleted article412 at midday I then need a table like so timestamp | user_id | subject_type | subject_id | method . there would be 5 potential methods to log, methods = add/edit/delete/update/report and lets say 2 possible subject_type subjects = article/comment I know i could make my own key where 0=add, 1=delete etc etc but this would make my queries cumbersome to use/write as i'd need to keep consulting the key. Is there a MySql type which can read lots of identially values quickly? is this ENUM? how do i use it?!!

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• How can I type cast EventArgs to have a .point property in c#? [closed]

  - by Sean Smyth

  I'm working with a double click function in c#. the function takes an object and EventArgs as it's parameters: private void gvHL7_DoubleClick(object sender, EventArgs e){ . . . } However, I want to use the .Point property, and EventArgs doesn't have that property. I know that DevExpress.XtraGrid.Views.Grid.GridMenuEventArgs does, but it's saying that's an invalid casting. What type should I cast my EventArgs instance to if I wish to access the .Point property? Edit: The double click function I'm working with is provided by devexpress for their grids.

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