Why does a Generic method with a “where T : class” constraint accept an interface

Question

I have this interface:

public interface ITestInterface
{
    int TestInt { get; set; }
}

and this generic method (with a

Answer 1

The class constraint means that the type must be a reference type, not necessarily a class.

From C# language specification:

The reference type constraint specifies that a type argument used for the type parameter must be a reference type. All class types, interface types, delegate types, array types, and type parameters known to be a reference type (as defined below) satisfy this constraint.

Basically, it means that the type cannot be a value type.

Value types can implement interfaces too, but casting a value type to an interface causes the value to be boxed

IComparable i = 0;

Now i stores a reference to a boxed 0.