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• Wildcards vs. generic methods

  - by FredOverflow

  Is there any practical difference between the following approaches to print all elements in a range? public static void printA(Iterable<?> range) { for (Object o : range) { System.out.println(o); } } public static <T> void printB(Iterable<T> range) { for (T x : range) { System.out.println(x); } } Apparently, printB involves an additional checked cast to Object (see line 16), which seems rather stupid to me -- isn't everything an Object anyway? public static void printA(java.lang.Iterable); Code: 0: aload_0 1: invokeinterface #18, 1; //InterfaceMethod java/lang/Iterable.iterator:()Ljava/util/Iterator; 6: astore_2 7: goto 24 10: aload_2 11: invokeinterface #24, 1; //InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object; 16: astore_1 17: getstatic #30; //Field java/lang/System.out:Ljava/io/PrintStream; 20: aload_1 21: invokevirtual #36; //Method java/io/PrintStream.println:(Ljava/lang/Object;)V 24: aload_2 25: invokeinterface #42, 1; //InterfaceMethod java/util/Iterator.hasNext:()Z 30: ifne 10 33: return public static void printB(java.lang.Iterable); Code: 0: aload_0 1: invokeinterface #18, 1; //InterfaceMethod java/lang/Iterable.iterator:()Ljava/util/Iterator; 6: astore_2 7: goto 27 10: aload_2 11: invokeinterface #24, 1; //InterfaceMethod java/util/Iterator.next:()Ljava/lang/Object; 16: checkcast #3; //class java/lang/Object 19: astore_1 20: getstatic #30; //Field java/lang/System.out:Ljava/io/PrintStream; 23: aload_1 24: invokevirtual #36; //Method java/io/PrintStream.println:(Ljava/lang/Object;)V 27: aload_2 28: invokeinterface #42, 1; //InterfaceMethod java/util/Iterator.hasNext:()Z 33: ifne 10 36: return

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• Linq generic Expression in query on "element" or on IQueryable (multiple use)

  - by Bogdan Maxim

  Hi, I have the following expression public static Expression<Func<T, bool>> JoinByDateCheck<T>(T entity, DateTime dateToCheck) where T : IDateInterval { return (entityToJoin) => entityToJoin.FromDate.Date <= dateToCheck.Date && (entityToJoin.ToDate == null || entityToJoin.ToDate.Value.Date >= dateToCheck.Date); } IDateInterval interface is defined like this: interface IDateInterval { DateTime FromDate {get;} DateTime? ToDate {get;} } and i need to apply it in a few ways: (1) Query on Linq2Sql Table: var q1 = from e in intervalTable where FunctionThatCallsJoinByDateCheck(e, constantDateTime) select e; or something like this: intervalTable.Where(FunctionThatCallsJoinByDateCheck(e, constantDateTime)) (2) I need to use it in some table joins (as linq2sql doesn't provide comparative join): var q2 = from e1 in t1 join e2 in t2 on e1.FK == e2.PK where OtherFunctionThatCallsJoinByDateCheck(e2, e1.FromDate) or var q2 = from e1 in t1 from e2 in t2 where e1.FK == e2.PK && OtherFunctionThatCallsJoinByDateCheck(e2, e1.FromDate) (3) I need to use it in some queries like this: var q3 = from e in intervalTable.FilterFunctionThatCallsJoinByDateCheck(constantDate); Dynamic linq is not something that I can use, so I have to stick to plain linq. Thank you Clarification: Initially I had just the last method (FilterFunctionThatCallsJoinByDateCheck(this IQueryable<IDateInterval> entities, DateTime dateConstant) ) that contained the code from the expression. The problem is that I get a SQL Translate exception if I write the code in a method and call it like that. All I want is to extend the use of this function to the where clause (see the second query in point 2)

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• Trouble rendering a view inside a generic class

  - by Horace Loeb

  I'm trying to encapsulate the logic for generating my sitemap in a separate class so I can use Delayed::Job to generate it out of band: class ViewCacher include ActionController::UrlWriter def initialize @av = ActionView::Base.new(Rails::Configuration.new.view_path) @av.class_eval do include ApplicationHelper end end def cache_sitemap songs = Song.all sitemap = @av.render 'sitemap/sitemap', :songs => songs Rails.cache.write('sitemap', sitemap) end end But whenever I try ViewCacher.new.cache_sitemap I get this error: ActionView::TemplateError: ActionView::TemplateError (You have a nil object when you didn't expect it! The error occurred while evaluating nil.url_for) on line #5 of app/views/sitemap/_sitemap.builder: I assume this means that ActionController::UrlWriter is not included in the right place, but I really don't know

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• Generic Lists copying references rather than creating a copiedList

  - by Dean

  I was developing a small function when trying to run an enumerator across a list and then carry out some action. (Below is an idea of what I was trying to do. When trying to remove I got a "Collection cannot be modified" which after I had actually woken up I realised that tempList must have just been assigned myLists reference rather than a copy of myLists. After that I tried to find a way to say tempList = myList.copy However nothing seems to exist?? I ended up writing a small for loop that then just added each item from myLsit into tempList but I would have thought there would have been another mechanism (like clone??) So my question(s): is my assumption about tempList receiving a reference to myList correct How should a list be copied to another list? private myList as List (Of something) sub new() myList.add(new Something) end sub sub myCalledFunction() dim tempList as new List (Of Something) tempList = myList Using i as IEnumerator = myList.getEnumarator while i.moveNext 'if some critria is met then tempList.remove(i.current) end end using end sub

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• c# Reflection - Find the Generic Type of a Collection

  - by Andy Clarke

  Hi, I'm reflecting a property 'Blah' its Type is ICollection public ICollection<string> Blah { get; set; } private void button1_Click(object sender, RoutedEventArgs e) { var pi = GetType().GetProperty("Blah"); MessageBox.Show(pi.PropertyType.ToString()); } This gives me (as you'd expect!) ICollection<string> ... But really I want to get the collection type i.e. ICollection (rather than ICollection<string>) - does anyone know how i'd do this please?

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• Call Javascript method from .ashx file

  - by Prasad Jadhav

  From my previous question(Create json using JavaScriptSerializer), In .ashx file I am printing the json object using: context.Response.ContentType = "application/json"; context.Response.Write(json); I am calling this .ashx file from default.aspx which has some javascript function inside its <head> tag. My question is : How will I be able to call the javascript function from .ashx file after context.Response.Write(json);?

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• Overloading generic implicit conversions

  - by raichoo

  Hi I'm having a little scala (version 2.8.0RC1) problem with implicit conversions. Whenever importing more than one implicit conversion the first one gets shadowed. Here is the code where the problem shows up: // containers class Maybe[T] case class Nothing[T]() extends Maybe[T] case class Just[T](value: T) extends Maybe[T] case class Value[T](value: T) trait Monad[C[_]] { def >>=[A, B](a: C[A], f: A => C[B]): C[B] def pure[A](a: A): C[A] } // implicit converter trait Extender[C[_]] { class Wrapper[A](c: C[A]) { def >>=[B](f: A => C[B])(implicit m: Monad[C]): C[B] = { m >>= (c, f) } def >>[B](b: C[B])(implicit m: Monad[C]): C[B] = { m >>= (c, { (x: A) => b } ) } } implicit def extendToMonad[A](c: C[A]) = new Wrapper[A](c) } // instance maybe object maybemonad extends Extender[Maybe] { implicit object MaybeMonad extends Monad[Maybe] { override def >>=[A, B](a: Maybe[A], f: A => Maybe[B]): Maybe[B] = { a match { case Just(x) => f(x) case Nothing() => Nothing() } } override def pure[A](a: A): Maybe[A] = Just(a) } } // instance value object identitymonad extends Extender[Value] { implicit object IdentityMonad extends Monad[Value] { override def >>=[A, B](a: Value[A], f: A => Value[B]): Value[B] = { a match { case Value(x) => f(x) } } override def pure[A](a: A): Value[A] = Value(a) } } import maybemonad._ //import identitymonad._ object Main { def main(args: Array[String]): Unit = { println(Just(1) >>= { (x: Int) => MaybeMonad.pure(x) }) } } When uncommenting the second import statement everything goes wrong since the first "extendToMonad" is shadowed. However, this one works: object Main { implicit def foo(a: Int) = new { def foobar(): Unit = { println("Foobar") } } implicit def foo(a: String) = new { def foobar(): Unit = { println(a) } } def main(args: Array[String]): Unit = { 1 foobar() "bla" foobar() } } So, where is the catch? What am I missing? Regards, raichoo

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• Create Generic Class Instance from Static Method in a Derived Class

  - by user343547

  I have a class in C# with a template and static method similar to class BClass<T> { public static BClass<T> Create() { return new BClass<T>(); } } From this I derive a class and specify a template parameter to the base class class DClass : BClass<int> { } A problem occurs when I try to use the static method to create an instance of D class Program { static void Main(string[] args) { DClass d = DClass.Create(); } } Gives a compiler error "Cannot implicitly convert type 'Test.BClass<int ' to 'Test.DClass'." Adding the below cast leads to a runtime casting exception. DClass d = (DClass)DClass.Create(); Is there any succint way to allow the static method to create instances of the derived class? Ideally I would like the equivalent of a c++ typedef and I don't want the below syntax (which does work). BClass<int> d = DClass.Create();

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• Creating a Type object corresponding to a generic type

  - by Alexey Romanov

  In Java, how can I construct a Type object for Map<String, String>? System.out.println(Map<String, String>.class); doesn't compile. One workaround I can think of is private Map<String, String> dummy() { throw new Error(); } Type mapStringString = Class.forName("ThisClass").getMethod("dummy", null).getGenericReturnType(); Is this the correct way?

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• generic Mysql stored procedure

  - by psu

  Hi, I have the fallowing stored procedure: CREATE PROCEDURE `get`(IN tb VARCHAR(50), IN id INTEGER) BEGIN SELECT * FROM tb WHERE Indx = id; END// When I call get(user,1) I get the following: ERROR 1054 (42S22): Unknown column 'user' in 'field list'

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• Generic JSON parser in .NET / WPF?

  - by niklassaers

  I've read lots of tutorials on how to deserialize a JSON object to an object of a particular using DataContractJsonSerializer. However, I'd like to deserialize my object to a Dictionary consisting of either Strings, Arrays or Dictionaries, such as System.Json does with SilverLight when I say JsonObject.Parse(myJSONstring). Is there an equivalent to System.Json that I can use in my WPF project? (just a short background: I'm fetching JSON objects that have way to much info, and I just want to use a little bit to fill out a String array) Cheers Nik

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• Exporting data to an accounting system for billing and invoicing - is there any generic standard pra

  - by Ali

  Hi guys, I've built a web application which basically logs work that has been done upon projects plus maintain resources used etc. What I need now is to set it up so that projects can be billed. Billed such that - each task that has been undertaken in a project is regarded as a billable service. Instead of building my own invoicing system and accounts management system I was wondering if there was any standard data format i.e in xml DTD or so to which I could set up the information so it could be imported by a third party accounting system for billing - or if not then what is the best way to accomplish this. I need to integrate invoicing capabilities somehow - better if its third party as I don't wish to have to go through building an entire accounting system.

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• Derived interface from generic method

  - by Sunit

  I'm trying to do this: public interface IVirtualInterface{ } public interface IFabricationInfo : IVirtualInterface { int Type { get; set; } int Requirement { get; set; } } public interface ICoatingInfo : IVirtualInterface { int Type { get; set; } int Requirement { get; set; } } public class FabInfo : IFabricationInfo { public int Requirement { get { return 1; } set { } } public int Type { get {return 1;} set{} } } public class CoatInfo : ICoatingInfo { public int Type { get { return 1; } set { } } public int Requirement { get { return 1; } set { } } } public class BusinessObj { public T VirtualInterface<T>() where T : IVirtualInterface { Type targetInterface = typeof(T); if (targetInterface.IsAssignableFrom(typeof(IFabricationInfo))) { var oFI = new FabInfo(); return (T)oFI; } if (targetInterface.IsAssignableFrom(typeof(ICoatingInfo))) { var oCI = new CoatInfo(); return (T)oCI; } return default(T); } } But getting a compiler error: Canot convert type 'GenericIntf.FabInfo' to T How do I fix this? thanks Sunit

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• An analog of String.Join(string, string[]) for List<T> or other generic enumerable

  - by abatishchev

  class String contains very useful method - String.Join(string, string[]). It creates a string from an array, separating each element of array with a symbol given. But general - it doesn't add a separator after the last element! I uses it for ASP.NET coding for separating with "<br />" or Environment.NewLine. So I want to add an empty row after each row in asp:Table. What method of IEnumerable<TableRow> can I use for the same functionality?

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• .NET XmlSerializer fails with List<T>

  - by Redshirt

  I'm using a singleton class to save all my settings info. It's first utilized by calling Settings.ValidateSettings(@"C:\MyApp"). The problem I'm having is that 'List Contacts' is causing the xmlserializer to fail to write the settings file, or to load said settings. If I comment out the List<T> then I have no problems saving/loading the xml file. What am I doing wrong? // The actual settings to save public class MyAppSettings { public bool FirstLoad { get; set; } public string VehicleFolderName { get; set; } public string ContactFolderName { get; set; } public List<ContactInfo> Contacts { get { if (contacts == null) contacts = new List<ContactInfo>(); return contacts; } set { contacts = value; } } private List<ContactInfo> contacts; } // The class in which the settings are manipulated public static class Settings { public static string SettingPath; private static MyAppSettings instance; public static MyAppSettings Instance { get { if (instance == null) instance = new MyAppSettings(); return instance; } set { instance = value; } } public static void InitializeSettings(string path) { SettingPath = Path.GetFullPath(path + "\\MyApp.xml"); if (File.Exists(SettingPath)) { LoadSettings(); } else { Instance.FirstLoad = true; Instance.VehicleFolderName = "Cars"; Instance.ContactFolderName = "Contacts"; SaveSettingsFile(); } } // load the settings from the xml file private static void LoadSettings() { XmlSerializer ser = new XmlSerializer(typeof(MyAppSettings)); TextReader reader = new StreamReader(SettingPath); Instance = (MyAppSettings)ser.Deserialize(reader); reader.Close(); } // Save the settings to the xml file public static void SaveSettingsFile() { XmlSerializer ser = new XmlSerializer(typeof(MyAppSettings)); TextWriter writer = new StreamWriter(SettingPath); ser.Serialize(writer, Settings.Instance); writer.Close(); } public static bool ValidateSettings(string initialFolder) { try { Settings.InitializeSettings(initialFolder); } catch (Exception e) { return false; } // Do some validation logic here return true; } } // A utility class to contain each contact detail public class ContactInfo { public string ContactID; public string Name; public string PhoneNumber; public string Details; public bool Active; public int SortOrder; }

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• Converting generic type to it's base and vice-versa

  - by Pajci

  Can someone help me with the conversion I am facing in enclosed code ... I commented the lines of code, where I am having problem. Is this even the right way to achieve this ... what I am trying to do, is forward responses of specified type to provided callback. public class MessageBinder { private class Subscriber<T> : IEquatable<Subscriber<T>> where T : Response { ... } private readonly Dictionary<Type, List<Subscriber<Response>>> bindings; public MessageBinder() { this.bindings = new Dictionary<Type, List<Subscriber<Response>>>(); } public void Bind<TResponse>(short shortAddress, Action<ZigbeeAsyncResponse<TResponse>> callback) where TResponse : Response { List<Subscriber<TResponse>> subscribers = this.GetSubscribers<TResponse>(); if (subscribers != null) { subscribers.Add(new Subscriber<TResponse>(shortAddress, callback)); } else { var subscriber = new Subscriber<TResponse>(shortAddress, callback); // ERROR: cannot convert from 'List<Subscriber<TResponse>>' to 'List<Subscriber<Response>>' ... tried LINQ Cast operator - does not work either this.bindings.Add(typeof(TResponse), new List<Subscriber<TResponse>> { subscriber }); } } public void Forward<TResponse>(TResponse response) where TResponse : Response { var subscribers = this.GetSubscribers<TResponse>(); if (subscribers != null) { Subscriber<TResponse> subscriber; Type responseType = typeof (TResponse); if (responseType.IsSubclassOf(typeof (AFResponse))) { // ERROR: Cannot convert type 'TResponse' to 'AFResponse' ... tried cast to object first, works, but is this the right way? var afResponse = (AFResponse)response; subscriber = subscribers.SingleOrDefault(s => s.ShortAddress == afResponse.ShortAddress); } else { subscriber = subscribers.First(); } if (subscriber != null) { subscriber.Forward(response); } } } private List<Subscriber<TResponse>> GetSubscribers<TResponse>() where TResponse : Response { List<Subscriber<Response>> subscribers; this.bindings.TryGetValue(typeof(TResponse), out subscribers); // ERROR: How can I cast List<Subscriber<Response>> to List<Subscriber<TResponse>>? return subscribers; } } Thank you for any help :)

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• Fastest way to check a List<T> for a date

  - by fishhead

  I have a list of dates that a machine has worked on, but it doesn't include a date that machine was down. I need to create a list of days worked and not worked. I am not sure of the best way to do this. I have started by incrementing through all the days of a range and checking to see if the date is in the list by iterating through the entire list each time. I am looking for a more efficient means of finding the dates. class machineday { datetime WorkingDay; } class machinedaycollection : List<machineday> { }

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• casting a generic array in java

  - by liloboy

  The implementation is for a linked list in java : public AnyType[] toArr() { AnyType[] arr = (AnyType[]) new Object[size]; int i = 0; Node<AnyType> current = head.next; while (cur != head){ arr[i] = current.data;// fill the array i++; current = current.next; } return arr; } public static void main(String[] args) { System.out.println(ll.toArr().toString()); } The error that I get: Exception in thread "main" java.lang.ClassCastException: [Ljava.lang.Object; cannot be cast to [Ljava.lang.Integer; Thanks.

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• Generic <T> how cast ?

  - by Kris-I

  Hi, I have a "Product" base class, some other classes "ProductBookDetail","ProductDVDDetail" inherit from this class. I use a ProductService class to make operation on these classes. But, I have to do some check depending of the type (ISBN for Book, languages for DVD). I'd like to know the best way to cast "productDetail" value, I receive in SaveOrupdate. I tried GetType() and cast with (ProductBookDetail)productDetail but that's not work. Thanks, var productDetail = new ProductDetailBook() { .... }; var service = IoC.Resolve<IProductServiceGeneric<ProductDetailBook>>(); service.SaveOrUpdate(productDetail); var productDetail = new ProductDetailDVD() { .... }; var service = IoC.Resolve<IProductServiceGeneric<ProductDetailDVD>>(); service.SaveOrUpdate(productDetail); public class ProductServiceGeneric<T> : IProductServiceGeneric<T> { private readonly ISession _session; private readonly IProductRepoGeneric<T> _repo; public ProductServiceGeneric() { _session = UnitOfWork.CurrentSession; _repo = IoC.Resolve<IProductRepoGeneric<T>>(); } public void SaveOrUpdate(T productDetail) { using (ITransaction tx = _session.BeginTransaction()) { //here i'd like ot know the type and access properties depending of the class _repo.SaveOrUpdate(productDetail); tx.Commit(); } } }

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• How to bind a ComboBox to generic dictionary with xaml code

  - by MMD MNC

  I'm using the following code : private Dictionary<string, string> GetNumber { get; set; } public ReportsLetterTra() { GetMonth = new Dictionary<string, string> { {"1", "First"}, {"2", "Second"} }; InitializeComponent(); } xaml code : <ComboBox DisplayMemberPath="value" SelectedValuePath="key" ItemsSource="{Binding ElementName=reportslettra,Path=GetNumber}" SelectedIndex="0" Name="cmbFromNumber" /> Why is not bind GetNumber to cmbFromNumber?!

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• How to declare a generic delegate with out parameter

  - by Benny

  Func<a, out b, bool>, just don't compile, how to declare that i want the second parameter be an out one?

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• Java weird generic return type

  - by drozzy

  Browsing through Guava libraries I saw this weird signature on a readLines method from Files class: public static <T> T readLines(File file, Charset charset, LineProcessor<T> callback) I know a little bit about generics in java, but this baffled me. What does the double T mean here? And why is the first one in angled brackets?

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• How to unit test generic classes

  - by Rowland Shaw

  I'm trying to set up some unit tests for an existing compact framework class library. However, I've fallen at the first hurdle, where it appears that the test framework is unable to load the types involved (even though they're both in the class library being tested) Test method MyLibrary.Tests.MyGenericClassTest.MyMethodTest threw exception: System.MissingMethodException: Could not load type 'MyLibrary.MyType' from assembly 'MyLibrary, Version=1.0.3778.36113, Culture=neutral, PublicKeyToken=null'.. My code is loosely: public class MyGenericClass<T> : List<T> where T : MyType, new() { public bool MyMethod(T foo) { throw new NotImplementedException(); } } With test methods: public void MyMethodTestHelper<T>() where T : MyType, new() { MyGenericClass<T> target = new MyGenericClass<T>(); foo = new T(); expected = true; actual = target.MyMethod(foo); Assert.AreEqual(expected, actual); } [TestMethod()] public void MyMethodTest() { MyMethodTestHelper<MyType>(); } I'm a bit stumped though, as I can't even get it to break in the debugger to get to the inner exception, so what else do I check? EDIT this does seem to be something specific to the Compact Framework - recompiling the class libraries and the unit tests for the full framework, gives the expected output (i.e. the debugger stops when I'm going to throw a NotImplementedException).

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• Linq to Sql: Generic Stored Procedures

  - by Eric

  Hello everyone, I am using Linq-to-Sql for a C# application and am currently working on some stored procedures. The application is for a newspaper, and a sample stored procedure is the following: ALTER PROCEDURE dbo.Articles_GetArticlesByPublication @publicationDate date AS SELECT * FROM Articles WHERE Articles.PublicationDate=@publicationDate Anyway, this query gets all of the articles where the publication date is equal to the argument (publicationDate). How can I alter this so that the argument can handle multiple publication dates? Also, I'd prefer not to use "BETWEEN," rather, I want to pick and choose dates.

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• Generic calls to OnResetDevice() and OnLostDevice()

  - by bobobobo

  This is kind of a COM question to do with DirectX. So, both ID3DXSprite and ID3DXFont and a bunch of the other ID3DX* objects require you to call OnLostDevice() when the d3d device is lost AND OnResetDevice() when the device is reset. What I want to do is maintain an array of all ID3DX* objects and simply call OnResetDevice() and OnLostDevice() on each whenever the device is lost or reset. However I can't seem to find a BASE CLASS for the ID3DX* classes... they all seem to COM-ually inherit from IUnknown. Is there a way to do this or do I have to maintain separate arrays of ID3DXFont* pointers, ID3DXSprite* pointers, etc?

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