Calling a static method on a generic type parameter

Question

I was hoping to do something like this, but it appears to be illegal in C#:

public Collection MethodThatFetchesSomething<T>()
    where T : SomeBaseClass
{
    return T.StaticMethodOnSomeBaseClassThatReturnsCollection();
}

I get a compile-time error: "'T' is a 'type parameter', which is not valid in the given context."

Given a generic type parameter, how can I call a static method on the generic class? The static method has to be available, given the constraint.

Answer 1

As of now, you can't. You need a way of telling the compiler that T has that method, and presently, there's no way to do that. (Many are pushing Microsoft to expand what can be specified in a generic constraint, so maybe this will be possible in the future).

Answer 2

It sounds like you're trying to use generics to work around the fact that there are no "virtual static methods" in C#.

Unfortunately, that's not gonna work.

Answer 3

The only way of calling such a method would be via reflection, However, it sounds like it might be possible to wrap that functionality in an interface and use an instance-based IoC / factory / etc pattern.

Answer 4

In this case you should just call the static method on the constrainted type directly. C# (and the CLR) do not support virtual static methods. So T.StaticMethodOnSomeBaseClassThatReturnsCollection can be no different than SomeBaseClass.StaticMethodOnSomeBaseClassThatReturnsCollection. Going through the generic type parameter is an unneeded indirection and hence not supported.

Answer 5

Here, i post an example that work, it's a workaround

public interface eInterface {
    void MethodOnSomeBaseClassThatReturnsCollection();
}

public T:SomeBaseClass, eInterface {

   public void MethodOnSomeBaseClassThatReturnsCollection() 
   { StaticMethodOnSomeBaseClassThatReturnsCollection() }

}

public Collection MethodThatFetchesSomething<T>() where T : SomeBaseClass, eInterface
{ 
   return ((eInterface)(new T()).StaticMethodOnSomeBaseClassThatReturnsCollection();
}