What does the keyword “where” in a class declaration do?

Question

I\'m looking at the source code for the MvcContrib Grid and see the class declared as:

public class Grid : IGrid where T : class


        

Answer 1

It restricts T to be a reference type, including any class, interface, delegate, or array type.

Answer 2

It's a generic type constraint. It specifies that the type T has to be a reference type, i.e. a class and not a structure.

Answer 3

It is a generic type constraint.

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

Other constraints are listed here.

You can also constrain the generic type to inherit from a specific type (base class or interface)

Answer 4

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

where T : class

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

Answer 5

It is a constraint on the type argument which says that T can either be a class or an interface but not an enum or a struct. So T must be a reference type and not a value type.

Best Regards,
Oliver Hanappi

Answer 6

you can apply restrictions to the kinds of types that client code can use for type arguments when it instantiates your class are called as Constraints on Type Parameters

E.g : where T : class

Here where T is the Type , The type argument must be a reference type; this applies also to any class, interface, delegate, or array type.