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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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  • What's the most efficient way to combine two List(Of String)?

    - by Jason Towne
    Let's say I've got: Dim los1 as New List(Of String) los1.Add("Some value") Dim los2 as New List(Of String) los2.Add("More values") What would be the most efficient way to combine the two into a single List(Of String)? Edit: While I'm loving the solutions everyone has provided so far, I probably should also mention I'm stuck using the .NET 2.0 framework. Any other suggestions?

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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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  • Is it possible to write a generic +1 method for numeric box types in Java?

    - by polygenelubricants
    This is NOT homework. Part 1 Is it possible to write a generic method, something like this: <T extends Number> T plusOne(T num) { return num + 1; // DOESN'T COMPILE! How to fix??? } Short of using a bunch of instanceof and casts, is this possible? Part 2 The following 3 methods compile: Integer plusOne(Integer num) { return num + 1; } Double plusOne(Double num) { return num + 1; } Long plusOne(Long num) { return num + 1; } Is it possible to write a generic version that bound T to only Integer, Double, or Long?

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  • Why can't these generic type parameters be inferred?

    - by Jon M
    Given the following interfaces/classes: public interface IRequest<TResponse> { } public interface IHandler<TRequest, TResponse> where TRequest : IRequest<TResponse> { TResponse Handle(TRequest request); } public class HandlingService { public TResponse Handle<TRequest, TResponse>(TRequest request) where TRequest : IRequest<TResponse> { var handler = container.GetInstance<IHandler<TRequest, TResponse>>(); return handler.Handle(request); } } public class CustomerResponse { public Customer Customer { get; set; } } public class GetCustomerByIdRequest : IRequest<CustomerResponse> { public int CustomerId { get; set; } } Why can't the compiler infer the correct types, if I try and write something like the following: var service = new HandlingService(); var request = new GetCustomerByIdRequest { CustomerId = 1234 }; var response = service.Handle(request); // Shouldn't this know that response is going to be CustomerResponse? I just get the 'type arguments cannot be inferred' message. Is this a limitation with generic type inference in general, or is there a way to make this work?

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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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  • 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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  • 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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  • 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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  • 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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  • Suggestions on Working with this Inherited Generic Method

    - by blu
    We have inherited a project that is a wrapper around a section of the core business model. There is one method that takes a generic, finds items matching that type from a member and then returns a list of that type. public List<T> GetFoos<T>() { List<IFoo> matches = Foos.FindAll( f => f.GetType() == typeof(T) ); List<T> resultList = new List<T>(); foreach (var match in matches) { resultList.Add((T)obj); } } Foos can hold the same object cast into various classes in inheritance hierarchy to aggregate totals differently for different UI presentations. There are 20+ different types of descendants that can be returned by GetFoos. The existing code basically has a big switch statement copied and pasted throughout the code. The code in each section calls GetFoos with its corresponding type. We are currently refactoring that into one consolidated area, but as we are doing that we are looking at other ways to work with this method. One thought was to use reflection to pass in the type, and that worked great until we realized the Invoke returned an object, and that it needed to be cast somehow to the List <T>. Another was to just use the switch statement until 4.0 and then use the dynamic language options. We welcome any alternate thoughts on how we can work with this method. I have left the code pretty brief, but if you'd like to know any additional details please just ask.

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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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  • 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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  • 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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  • 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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  • 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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  • 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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  • 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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  • Generic object comparison diff routine

    - by MicMit
    The question stems from database tables comparison. Let's say we put left row in the instance Left and the right one into instance Right of the same type. And we'got many tables and respective types. How to implement more or less generic routine resulting in a collection of diffs e.g. propertyName , leftValue , rightValue for each such a pair of instances of the same type.

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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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