opCast for classes

[Luís.Marques]

Hi there,

I've been away for a while from the D world, so I guess I missed 
some of the new things.

Regarding opCast, the documentation says:

"This only happens, however, for instances of structs. Class 
references are converted to bool by checking to see if the class 
reference is null or not."

Yet this works:

class B
{
    bool v;

    this(bool v)
    {
        this.v = v;
    }

    T opCast(T)()
    {
        return v;
    }
}

unittest
{
    B bfalse = new B(false);
    B btrue = new B(true);
    assert(cast(bool) bfalse == false);
    assert(cast(bool) btrue == true);
}

Is that a new feature? Can I rely on it? Is it documented 
somewhere?

Thanks! :-)

Regards,
Luís