Question

What is the difference between these method signatures?

public void T MyMethod<T>(T parameter)

and

public void T MyMethod<T>(T parameter) where T : class

They seem to have the same result … so what does where T : class do?

Answer 1

In the second method the T can only be a class and cannot be a structure type.

See Constraints on Type Parameters (C# Programming Guide):

where T : class

The type argument must be a reference [class] type; this applies also to any class, interface, delegate, or array type.