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• AS3: why is this happening?

  - by Bin Chen

  Hi, I just encounter a strange problem: var a:ClassA = new ClassA; var b:ClassA = a; The program keeps running sometime, the a = null, b = null. The program is a complex one, I am sure that no part will touch a, and b. My question is, will the runtime(garbage collector) to collect the memory of "a" and then assign a and b to null? I am confused, thanks!

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• WeakHashMap iteration and garbage collection

  - by Shamik

  I am using a WeaekHashMap to implement a Cache. I am wondering if I am iterating over the keys of this map, and at the same time garbage collector is actively removing keys from this map, would I receive a ConcurrentModificationException ? I do not think so, because as far as I understand, concurrentmodificationexception happens because of bugs in the application code where the developer forgot to understand that the same map is shared/used by other threads and in this case, it should not happen. But wondering how would JVM handle this when WeakHashMap is not synchronized ?

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• Comparing the values of two generic Numbers

  - by PartlyCloudy

  I want to compare to variables, both of type T extends Number. Now I want to know which of the two variables is greater than the other or equal. Unfortunately I don't know the exact type yet, I only know that it will be a subtype of java.lang.Number. How can I do that? Thanks!

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• I want to make my own Malloc

  - by Unknown

  I want to make my own malloc/free so I can make a precise copying allocator. Any gurus have any tips and suggestions? I have a few questions for now: Should I just malloc large chunks of memory, and then distribute from that so I don't have to call the system calls? How are copying collectors usually done? I would imagine that this part is a bit complicated to do efficiently. My naive implementation would just malloc a block the size of the remaining objects which would require 2x the space.

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• Why isn't the new() generic constraint satisfied by a class with optional parameters in the construc

  - by Joshua Flanagan

  The following code fails to compile, producing a "Widget must be a non-abstract type with a public parameterless constructor" error. I would think that the compiler has all of the information it needs. Is this a bug? An oversight? Or is there some scenario where this would not be valid? public class Factory<T> where T : new() { public T Build() { return new T(); } } public class Widget { public Widget(string name = "foo") { Name = name; } public string Name { get; set; } } public class Program { public static void Main() { var widget = new Widget(); // this is valid var factory = new Factory<Widget>(); // compiler error } }

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• Overriding inherited generic methods

  - by jess

  I have this code in base class protected virtual bool HasAnyStuff<TObject>(TObject obj) where TObject:class { return false; } In child class I am overriding protected override bool HasAnyStuff<Customer>(Customer obj) { //some stuff if Customer.sth etc return false; } I am getting this error '''Type parameter declaration must be an identifier not a type''' What is it I am doing wrong here?

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• How do you create a nested LINQ Grouping / Lookups for a Collection of Objects

  - by Jeff Windsor

  Given a list of objects with a date and decimal, I would like to index these objects by the year, month, dayofweek and hour of the date. In .NET 2.0, I would have created this graph using a set of nested dictionaries and a list as the leaf node. I am interested in how this could be done with LINQ.

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• IList<T> versus Collection<T> as property

  - by Brian Triplett

  I have a class with a internal array field. I want to expose this array as a property, such that it maintains as much funtionallity of the orginal array but does not violate abstraction by exposing the array directly. What are the various methods and pros and cons? I'm thinking specifically about IList<T> or Colleciton<T>

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• C# Possible to have a generic return type?

  - by JL

  Here is a typical function that returns either true/false; private static bool hasValue() { return true; } Now on an error, I would like to return my own custom error object with definition: public class Failure { public string failureDateTime { get; set; } public string failureReason { get; set; } } I would have expected to be able to throw this custom object for example... private static bool hasValue() { throw new Failure(); } This is not possible, and I don't want to derive Failure from System.IO.Exception because of the inability to serialize an exception in C#. What is the best practice / or ideal solution to this problem. Should I just work with private static object? Or is there a cleaner way to return a custom object or bypass the typical return type on an error (not using System.IO.Exception)? Not entirely wild about object either, because then I need to cast the result and validate it by more boolean logic.

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• A strange error in java generic.

  - by ???

  This is ok: Class<? extends String> stringClass = "a".getClass(); But this gets error: <T> void f(T obj) { Class<? extends T> objClass = obj.getClass(); } I know I can cast it like: <T> void f(T obj) { @SuppressWarnings("unchecked") Class<? extends T> objClass = (Class<? extends T>) obj.getClass(); } But why the previous error? Will the next release of Java 7 will support such usage?

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• C# determining generic type

  - by Chris Klepeis

  I have several templated objects that all implement the same interface: I.E. MyObject<datatype1> obj1; MyObject<datatype2> obj2; MyObject<datatype3> obj3; I want to store these objects in a List... I think I would do that like this: private List<MyObject<object>> _myList; I then want to create a function that takes 1 parameter, being a datatype, to see if an object using that datatype exists in my list.... sorta clueless how to go about this. In Pseudo code it would be: public bool Exist(DataType T) { return (does _myList contain a MyObject<T>?); }

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• Generic Vector in Java

  - by portoalet

  Hi, Why doesn't the add() method here compile? Vector<?> vectorList[] = new Vector<?>[10]; vectorList[0].add("elem1"); Thanks

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• C# - free all resources used by an object

  - by user1112111

  Is there some way to free all resources used by certain object ? If not, why wouldn't I use the GC.Collect() method ?

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• Generic DRM (Distributed resource management) wrapper

  - by Pavel Bernshtam

  I need to write a software, which launches DRM jobs in a customer environment and monitors those jobs status. It should work with various customer environments and DRMs - like LSF, Sun Grid and others. Can you recommend some 3rd party library, which hides DRM differences from me and has API like "launch job", "get list of jobs", "get job status" etc. ? Both Java and native libraries are good for me.

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• How to create a generic Android XML layout for all activities

  - by zabawaba

  I have an application that needs the same items [5 buttons acting as tabs] in every screen. Is it possible to create a "base XML layout" that has these 5 buttons and then have all the other XML files extend from the bas layout in some way so that I don't have to have multiple buttons that will ultimately have the same functionality. Is there a better approach to this problem that can be supported by API 9

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• List.ForEach method and collection interfaces

  - by tyndall

  In .NET 3.5 List< gains a ForEach method. I notice this does not exist on IList< or IEnumerable< what was the thinking here? Is there another way to do this? Nice and simple short way to do this? I ask because I was at a talk where the speaker said always use the more general interfaces. But why would I use IList< as a return type if I want to be able to turn around and use ForEach? Then I would just end up casting it back to a List<.

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• [Scala] Using overloaded, typed methods on a collection

  - by stephanos

  I'm quite new to Scala and struggling with the following: I have database objects (type of BaseDoc) and value objects (type of BaseVO). Now there are multiple convert methods (all called 'convert') that take an instance of an object and convert it to the other type accordingly. For example: def convert(doc: ClickDoc): ClickVO = doc match { case null => null case _ => val result = new ClickVO result.x = doc.x result.y = doc.y result } Now I sometimes need to convert a list of objects. How would I do this - I tried: def convert[D <: MyBaseDoc, V <: BaseVO](docs: List[D]):List[V] = docs match { case List() => List() case xs => xs.map(doc => convert(doc)) } Which results in 'overloaded method value convert with alternatives ...'. I tried to add manifest information to it, but couldn't make it work. I couldn't even create one method for each because it'd say that they have the same parameter type after type erasure (List). Ideas welcome!

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• [Scala] Applying overloaded, typed methods on a collection

  - by stephanos

  I'm quite new to Scala and struggling with the following: I have database objects (type of BaseDoc) and value objects (type of BaseVO). Now there are multiple convert methods (all called 'convert') that take an instance of an object and convert it to the other type accordingly - like this: def convert(doc: ClickDoc): ClickVO = ... def convert(doc: PointDoc): PointVO = ... def convert(doc: WindowDoc): WindowVO = ... Now I sometimes need to convert a list of objects. How would I do this - I tried: def convert[D <: BaseDoc, V <: BaseVO](docs: List[D]):List[V] = docs match { case List() => List() case xs => xs.map(doc => convert(doc)) } Which results in 'overloaded method value convert with alternatives ...'. I tried to add manifest information to it, but couldn't make it work. I couldn't even create one method for each because it'd say that they have the same parameter type after type erasure (List). Ideas welcome!

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• Ruby On Rails - Collection Select - MYSQL Database - Problem Displaying ampersand ("&")

  - by dbkbaki

  I am having an annoying problem displaying the labels of a select box correctly where there is an ampersand contained within the label string. On a form being rendered with the form_for helper the collection_select reads data from a Mysql 5.075 database the text stored in the database is "Surabaya & Surrounding Areas" when rendered and displayed in firefox 3.6 or safari is is displaying as "Surabaya %amp; Surrounding Areas". The code used to render the select is as follows: <%= f.collection_select :parent_id, Destination.roots, :id, :name, {:include_blank => true} %> I have tried adding a h(:name) and also storing && in the database but it still will not display the ampersand correctly. Have searched on google for what I thought would be a simple solution but cant find anything that solves this. Using ROR 2.3.5/Ruby 1.8.7 If anyone has a solution it will be much appreciated. many thanks, David

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• How Can I Accept a Generic Class and Use Its Properties / Methods

  - by Blake Blackwell

  I want to create a class that could hold any of a number of same type of classes. For example lets says I have a base class like follows: public class BaseClass { public string MyBaseString { get; set; } } And then I have a few derived classes like this: public class DerivedClass : BaseClass { public MyDerivedClassString { get; set; } } public class DerivedClass2 : BaseClass { public MyDerivedClass2String { get; set; } } Now I would like a class that accepts one of these implementations and does stuff with it. Here is the only thing I can think of, but there must be a better way: public class ClassA { public object MyClass { get; set; } public ClassA (object myClass) { MyClass = myClass; if (object is BaseClass) { //do something } else if (object is DerivedClass) { //do something specific to derived class } else if (object is DerivedClass2) { //do something specific to derived class 2 } } } I'm not sure really what I'm looking for here. Any ideas would be great!

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• How online-game clients are able to exchange data through internet so fast?

  - by Kirzilla

  Hello, Let's imagine really simple game... We have a labirinth and two players trying to find out exit in real time through internet. On every move game client should send player's coordinates to server and accept current coordinates of another client. How is it possible to make this exchange so fast (as all modern games do). Ok, we can use memcache or similar technology to reduce data mining operations on server side. We can also use fastest webserver etc., but we still will have problems with timings. So, the questions are... What protocol game clients are usually using for exchanging information with server? What server technologies are coming to solve this problem? What algorithms are applied for fighting with delays during game etc. PS: Sorry for my English and I hope that my question is clear. Thank you.

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• Passing a generic class to a java function?

  - by rodo

  Is it possible to use Generics when passing a class to a java function? I was hoping to do something like this: public static class DoStuff { public <T extends Class<List>> void doStuffToList(T className) { System.out.println(className); } public void test() { doStuffToList(List.class); // compiles doStuffToList(ArrayList.class); // compiler error (undesired behaviour) doStuffToList(Integer.class); // compiler error (desired behaviour) } } Ideally the List.class and ArrayList.class lines would work fine, but the Integer.class line would cause a compile error. I could use Class as my type instead of T extends Class<List> but then I won't catch the Integer.class case above.

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• Dispatching generic tasks in WCF or .Net Remoting

  - by Eric

  Hello all, I've been researching for a couple days on and off, and have yet to figure out the best way to achieve the following goal. I would like to define either an interface or abstract class in C# which has an associated Run method, similar to the Java runnable interface. The goal would be to have a shared queue which contains a list of these objects. Then individual clients would be able to derive their own concrete runnable classes and add them to the queue hosted by the server. Clients would also be able to pop these runnable objects off the queue and execute them arbitrarily. This seems like it should be feasible in a VM based language without needing to place any of the concrete implementations in a shared assembly, but I have thus far had no luck finding a working example of such a system. Does anyone know how this might be achieved?

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• implict type cast in generic method

  - by bitbonk

  why do I get a compiler error in the following code stating: Cannot implicty convert type SpecialNode to T even though T must derive from NodeBase as I defined in the where clause and even though SpecialNode actually derived from NodeBase? public static T GetNode<T>() where T : NodeBase { if (typeof(T) == typeof(SpecialNode)) { return ThisStaticClass.MySpecialNode; // <-- compiler error } if (typeof(T) == typeof(OtherSpecialNode)) { return ThisStaticClass.MyOtherSpecialNode; // <-- compiler error } ... return default(T); }

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• Linq based generic alternate to Predicate<T>?

  - by Eric

  I have an interface called ICatalog as shown below where each ICatalog has a name and a method that will return items based on a Predicate<Item> function. public interface ICatalog { string Name { get; } IEnumerable<IFamily> GetItems(Predicate<Item> predicate); } A specific implementation of a catalog may be linked to catalogs in various format such as XML, or a SQL database. With an XML catalog I end up deserializing the entire XML file into memory, so testing each item with the predicate function does does not add a whole lot more overhead as it's already in memory. Yet with the SQL implementation I'd rather not retrieve the entire contents of the database into memory, and then filter the items with the predicate function. Instead I'd want to find a way to somehow pass the predicate to the SQL server, or somehow convert it to a SQL query. This seems like a problem that can be solved with Linq, but I'm pretty new to it. Should my interface return IQueryable instead?

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