In c# what does 'where T : class' mean?

Question

In C# what does where T : class mean?

Ie.

public IList DoThis() where T : class

Answer 1

It is a generic type constraint. In this case it means that the generic type T has to be a reference type (class, interface, delegate, or array type).

Answer 2

That restricts T to reference types. You won't be able to put value types (structs and primitive types except string) there.

Answer 3

it means that the type used as T when the generic method is used must be a class - i.e. it cannot be a struct or built in number like int or double

// Valid:
var myStringList = DoThis<string>();
// Invalid - compile error
var myIntList = DoThis<int>();

Answer 4

'T' represents a generic type. It means it can accept any type of class. The following article might help:

http://www.15seconds.com/issue/031024.htm