What is "where T : class" in C# generic methods?

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.

Answer 2

in the first one you can call it with a non ref type for example

MyMethod<int>(10);

that will not work with the second version as it only accepts ref types!

Answer 3

there is no difference, but T is restricted to a reference-type. they differ only at compiletime, as the compiler checks wether T is a ref-type or not.

Answer 4

1. Both won't compile. You should use either void or T.
2. And second method won't work for MyMethod(1) because it requires reference type to T