如何传递给实现certan接口的泛型函数类类型？

Question

I want to create a generic function with signature like this : void funcName<T>() where T would be required to be an implementation of some particular interface I want. How to make such check? How to pass to a generic function class type that implements certan interface?

So I create some public interface IofMine {} and I try to create a function like public static void funcName<T>() where T : IofMine { var a = new T} and sadly I get:

Error: Cannot create an instance of the variable type 'T' because it does not have the new() constraint

What shall I do to make class types my function receives not only be of my desired interface but also have a constructor?

Answer 1

In order to require that the generic parameter have a default constructor, specify new() as part of the generic constraint.

public static void funcName<T>() where T : IofMine, new()
{
    T a = new T();
}

You can only use this to require a default (ie, no parameters) constructor. You can't require a constructor taking a string parameter, for example.

Answer 2

Simple:

public void FuncName<T>(...) 
    where T : IMyInterface
{
    ...
}

This creates a constraint on the type parameter T so that any type used when calling the method must implement IMyInterface .

Answer 3

This is how you declare it:

// Let's say that your function takes
// an instance of IMyInterface as a parameter:
void funcName<T>(T instance) where T : IMyInterface {
    instance.SomeInterfaceMethodFromMyInterface();
}

This is how you call it:

IMyInterface inst = new MyImplOfMyInterface();
funcName(inst);

Answer 4

If I understood you correct, you need to use constraints of generic:

public interface TestInterface
{
}

public void func<T>()
    where T : TestInterface
{ 

}

http://msdn.microsoft.com/en-us/library/d5x73970.aspx