I have this interface:
public interface ITestInterface
{
int TestInt { get; set; }
}
and this generic method (with a T : class constraint):
public void Test<T>() where T : class
{
// DoSomething
}
and this call:
Test<ITestInterface>();
and everything compiles and runs while an interface is not a class (or is it?).
Why does this happen?
I first saw this on my WCF proxy class:
public partial class TestServiceClient:
System.ServiceModel.ClientBase<TestNamespace.ITestService>, TestNamespace.ITestService
where ClientBase<T> has this definition:
public abstract class ClientBase<TChannel> :
ICommunicationObject, IDisposable where TChannel : class
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.
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