How can a value type implement an interface type?

Question

In the C# Language Specification v5.0, in section 1.3, it says this:

An Interface type can have as its contents a null reference, a reference to an instance of a class type that implements that interface type, or a reference to a boxed value of a value type that implements that interface type

I have no problem with two out of three of those statements. However, the last one confuses me. How can an interface type hold a boxed value of a value type that implements that interface type? I thought value types couldn't implement interface types? Or is it saying that the boxed value implements the interface type? If that's the case, how can a boxed value implement an interface type?

I'm having a spot of trouble comprehending all of this.

Answer 1

Value type (struct) can implement interface. It cannot inherit another struct, but can implement interface.

struct (C# Reference)

Structs can implement an interface but they cannot inherit from another struct. For that reason, struct members cannot be declared as protected.

So when you have a struct which implements IInterface and you do following:

var value = new MyStruct();
var valueAsInterface = (IInterface)value;

valueAsInterface contains reference to a boxed value of a value type that implements that interface type.

Answer 2

There's nothing that says that a value type can't implement an interface.

The following code is perfectly legal:

interface ITest
{
    void DoSomething();
}

struct MyTest : ITest
{
    public void DoSomething()
    {
        // do something
    }
}