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• How do I get the type name of a generic type argument?

  - by Tomas Lycken

  If I have a method signature like public string myMethod<T>( ... ) How can I, inside the method, get the name of the type that was given as type argument? I'd like to do something similar to typeof(T).FullName, but that actually works...

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• Operation Problems in Java Generic

  - by alantheweasel

  I got some problem when i was learning Java Generic : interface calculator<T, R> { public void execute(T t, R r); } class executeAdd<T, R> implements calculator<T, R> { private T first; private R second; public executeAdd(T first, R second) { super(); this.first = first; this.second = second; } @Override public void execute(T t, R r) { // TODO Auto-generated method stub Object o = t + r // ERROR ! What i could do it ? } }

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• Generic Event Generator and Handler from User Supplied Types?

  - by JaredBroad

  I'm trying to allow the user to supply custom data and manage the data with custom types. The user's algorithm will get time synchronized events pushed into the event handlers they define. I'm not sure if this is possible but here's the "proof of concept" code I'd like to build. It doesn't detect T in the for loop: "The type or namespace name 'T' could not be found" class Program { static void Main(string[] args) { Algorithm algo = new Algorithm(); Dictionary<Type, string[]> userDataSources = new Dictionary<Type, string[]>(); // "User" adding custom type and data source for algorithm to consume userDataSources.Add(typeof(Weather), new string[] { "temperature data1", "temperature data2" }); for (int i = 0; i < 2; i++) { foreach (Type T in userDataSources.Keys) { string line = userDataSources[typeof(T)][i]; //Iterate over CSV data.. var userObj = new T(line); algo.OnData < typeof(T) > (userObj); } } } //User's algorithm pattern. interface IAlgorithm<TData> where TData : class { void OnData<TData>(TData data); } //User's algorithm. class Algorithm : IAlgorithm<Weather> { //Handle Custom User Data public void OnData<Weather>(Weather data) { Console.WriteLine(data.date.ToString()); Console.ReadKey(); } } //Example "user" custom type. public class Weather { public DateTime date = new DateTime(); public double temperature = 0; public Weather(string line) { Console.WriteLine("Initializing weather object with: " + line); date = DateTime.Now; temperature = -1; } } }

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• Why does this static factory method involving implied generic types, work?

  - by Cheeso

  Consider public class Tuple<T1, T2> { public Tuple(T1 v1, T2 v2) { V1 = v1; V2 = v2; } public T1 V1 { get; set; } public T2 V2 { get; set; } } public static class Tuple { // MAGIC!! public static Tuple<T1, T2> New<T1, T2>(T1 v1, T2 v2) { return new Tuple<T1, T2>(v1, v2); } } Why does the part labeled "MAGIC" in the above work? It allows syntax like Tuple.New(1, "2") instead of new Tuple<int, string>(1, "2"), but ... how and why? Why do I not need Tuple.New<int,string>(1, "2") ??

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

  - by this. __curious_geek

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

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• (Action<T>).Name does not return expected values

  - by Tomas Lycken

  I have the following method (used to generate friendly error messages in unit tests): protected string MethodName<TTestedType>(Action<TTestedType> call) { return string.Format("{0}.{1}", typeof(TTestedType).FullName, call.Method.Name); } But when I call it as follows, I don't get the expected results: var nm = MethodName<MyController>(ctrl => ctrl.Create()); After running this code, nm contains "<Create_CreateShowsView>b__8", and not (as expected) "Create". How should I change the code to obtain the expected result?

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• What CLR do when compare T with null, and T is a struct?

  - by Fujiy

  private static void SaveOrRemove<T>(string key, T value) { if (value == null) { Console.WriteLine("Remove: " +key); } .... } If I call passing 0 to value: SaveOrRemove("MyKey", 0), the condition (value == null) is false, then CLR dont make a (value == default(T)). What really happens?

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• How can I define a constructor in an open generic type?

  - by Cort

  I am trying to create on open generic type that has a constructor to be used by derived types, but I either don't know how to do it or it is not possible -- not sure which. public struct DataType<T> : IDataType { private T myValue; private TypeState myState; private DataType<T>(T initialValue, TypeState state) { myValue = initialValue; myState = state; } } Any help much appreciated! Cort

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• Generic Dictionary - Getting Conversion Error

  - by pm_2

  The following code is giving me an error: // GetDirectoryList() returns Dictionary<string, DirectoryInfo> Dictionary<string, DirectoryInfo> myDirectoryList = GetDirectoryList(); // The following line gives a compile error foreach (Dictionary<string, DirectoryInfo> eachItem in myDirectoryList) The error it gives is as follows: Cannot convert type 'System.Collections.Generic.KeyValuePair<string,System.IO.DirectoryInfo>' to 'System.Collections.Generic.Dictionary<string,System.IO.DirectoryInfo>’ My question is: why is it trying to perform this conversion? Can I not use a foreach loop on this type of object?

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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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• How to get all possible generic type in StructureMap?

  - by Soul_Master

  I just used StructureMap few days ago. I use StructureMap for collecting all validator class like the following code. public class BaseClassA {} public class ClassB : BaseClassA {} public class ClassC : BaseClassB {} public BaseClassAValidator : IValidator<BaseClassA>() {} In StructureMap, I only register IValidator interface for BaseClassAValidator class. But I want to get the same result when I call IValidator or IValidator that mean StructureMap should return IValidator where T is requested class or parent class of requested class. Is it possible? Or I need to manually call it.

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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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• Why does my WCF service return and ARRAY instead of a List <T> ?

  - by user193189

  In the web servce I say public List<Customer> GetCustomers() { PR1Entities dc = new PR1Entities(); var q = (from x in dc.Customers select x).ToList(); return q; } (customer is a entity object) Then I generate the proxy when I add the service.. and in the reference.cd it say public wcf1.ServiceReference1.Customer[] GetCustomers() { return base.Channel.GetCustomers(); } WHY IS IT AN ARRAY? I asked for a List. help.

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• is this possible: c# collection of Type with constrains, or collection of generic type?

  - by Jon

  I'm trying to store types in a collection, so that i can later instantiate objects of the types in the collection. But I'm not sure how to do this the best way. What i have so far: List<Type> list = new List<Type>(); list.Add(typeof(MyClass)); var obj = (MyClass)Activator.CreateInstance(list[0]); I would like to have some constrains on the Type, or better yet, just a generic type in the collection instead of an instantiated Type object. Is this possible?

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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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• Decrement all int values in Dictionary

  - by Jon

  I have a Dictionary<string,int> and I simply want to decrement the value in my dictionary by one. I have this but not sure if its best practice. foreach (KeyValuePair<string, int> i in EPCs) { EPCs[i.Key] = i.Value - 1; }

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• Catch a generic exception in Java?

  - by Alex Baranosky

  We use JUnit 3 at work and there is no ExpectedException annotation. I wanted to add a utility to our code to wrap this: try { someCode(); fail("some error message"); } catch (SomeSpecificExceptionType ex) { } So I tried this: public static class ExpectedExceptionUtility { public static <T extends Exception> void checkForExpectedException(String message, ExpectedExceptionBlock<T> block) { try { block.exceptionThrowingCode(); fail(message); } catch (T ex) { } } } However, Java cannot use generic exception types in a catch block, I think. How can I do something like this, working around the Java limitation? Is there a way to check that the ex variable is of type T?

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• Using overloaded operator== in a generic function

  - by Dimitri C.

  Consider the following code: class CustomClass { public CustomClass(string value) { m_value = value; } public static bool operator==(CustomClass a, CustomClass b) { return a.m_value == b.m_value; } public static bool operator!=(CustomClass a, CustomClass b) { return a.m_value != b.m_value; } public override bool Equals(object o) { return m_value == (o as CustomClass).m_value; } public override int GetHashCode() { return 0; /* not needed */ } string m_value; } class G { public static bool enericFunction1<T>(T a1, T a2) where T : class { return a1.Equals(a2); } public static bool enericFunction2<T>(T a1, T a2) where T : class { return a1==a2; } } Now when I call both generic functions, one succeeds and one fails: var a = new CustomClass("same value"); var b = new CustomClass("same value"); Debug.Assert(G.enericFunction1(a, b)); // Succeeds Debug.Assert(G.enericFunction2(a, b)); // Fails Apparently, G.enericFunction2 executes the default operator== implementation instead of my override. Can anybody explain why this happens?

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• Generic collection class?

  - by Mark

  Is there anyway I can do this? class TSOC<TCollection, TValue> : ICollection<TValue>, INotifyCollectionChanged where TCollection : ICollection { private TCollection<TValue> collection; } It doesn't like my definition of collection. I'd prefer the definition to look like TSOC<TCollection> where the user can pass in List<int> or something, but then I need to pull out the "int" to know what interface to implement.

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• How can I add to List<? extends Number> data structures?

  - by kunjaan

  I have a List which is declared like this : List<? extends Number> foo3 = new ArrayList<Integer>(); I tried to add 3 to foo3. However I get an error message like this: The method add(capture#1-of ? extends Number) in the type List<capture#1-of ? extends Number> is not applicable for the arguments (ExtendsNumber)

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• List of Lists of different types

  - by themarshal

  One of the data structures in my current project requires that I store lists of various types (String, int, float, etc.). I need to be able to dynamically store any number of lists without knowing what types they'll be. I tried storing each list as an object, but I ran into problems trying to cast back into the appropriate type (it kept recognizing everything as a List<String>). For example: List<object> myLists = new List<object>(); public static void Main(string args[]) { // Create some lists... // Populate the lists... // Add the lists to myLists... for (int i = 0; i < myLists.Count; i++) { Console.WriteLine("{0} elements in list {1}", GetNumElements(i), i); } } public int GetNumElements(int index) { object o = myLists[index]; if (o is List<int>) return (o as List<int>).Count; if (o is List<String>) // <-- Always true!? return (o as List<String>).Count; // <-- Returning 0 for non-String Lists return -1; } Am I doing something incorrectly? Is there a better way to store a list of lists of various types, or is there a better way to determine if something is a list of a certain type?

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• Select a Dictionary<T1, T2> with LINQ

  - by Rich

  I have used the "select" keyword and extension method to return an IEnumerable<T> with LINQ, but I have a need to return a generic Dictionary<T1, T2> and can't figure it out. The example I learned this from used something in a form similar to the following: IEnumerable<T> coll = from x in y select new SomeClass{ prop1 = value1, prop2 = value2 }; I've also done the same thing with extension methods. I assumed that since the items in a Dictionary<T1, T2> can be iterated as KeyValuePair<T1, T2> that I could just replace "SomeClass" in the above example with "new KeyValuePair<T1, T2> { ...", but that didn't work (Key and Value were marked as readonly, so I could not compile this code). Is this possible, or do I need to do this in multiple steps? Thanks.

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• What is the best way to write class template-like generic code in C?

  - by Ribtoks

  I need to write AVL-tree with generic type in C. The best way I know is to use [ void* ] and to write some functions for creating, copying, assignment and destruction. Please, tell me some better way.

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• How to return a value based on the type of the generic T

  - by Blankman

  I have a method like: public T Get<T>(string key) { } Now say I want to return "hello" if the type is a string, and 110011 if it is type int. how can I do that? typeof(T) doesn't seem to work. I ideally want to do a switch statement, and return something based on the Type of the generic (string/int/long/etc). Is this possible?

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• Call Generic method using runtime type and cast return object

  - by markpirvine

  I'm using reflection to call a generic method with a type determined at runtime. My code is as follows: Type tType = Type.GetType(pLoadOut.Type); MethodInfo method = typeof(ApiSerialiseHelper).GetMethod("Deserialise", new Type[] { typeof(string) }); MethodInfo generic = method.MakeGenericMethod(tType); generic.Invoke(obj, new object[] { pLoadOut.Data }); This works ok. However the generic.Invoke method returns an object, but what I would like is the type determined at runtime. Is this possible with this approach, or is there a better option? Mark

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