Structs, Interfaces and Boxing

Question

Possible Duplicate:
Is it safe for structs to implement interfaces?

Take this code:

interface ISomeInterface
{
    public int SomeProperty { get; }
}

struct SomeStruct : ISomeInterface
{
    int someValue;

    public int SomeProperty { get { return someValue; } }

    public SomeStruct(int value)
    {
        someValue = value;
    }
}

and then I do this somewhere:

ISomeInterface someVariable = new SomeStruct(2);

is the SomeStruct boxed in this case?

Answer 1

Jon's point is true, but as a side note there is one slight exception to the rule; generics. If you have where T : ISomeInterface, then this is constrained, and uses a special opcode. This means the interface can be used without boxing. For example:

public static void Foo<T>(T obj) where T : ISomeInterface {
    obj.Bar(); // Bar defined on ISomeInterface
}

This does not involve boxing, even for value-type T. However, if (in the same Foo) you do:

ISomeInterface asInterface = obj;
asInterface.Bar();

then that boxes as before. The constrained only applies directly to T.