Re: putting more smarts into a == b

[Andrei Alexandrescu]

Frank Benoit wrote:
Andrei Alexandrescu schrieb:
Consider two objects a and b with a of class type. Currently, the
expression a == b is blindly rewritten as a.opEquals(b). I argue it
should be rewritten into a call to an (imaginary/inlined) function
equalObjects(a, b), with the following definition:
bool equalObjects(T, U)(T a, U b) if (is(T == class))
{
    static if (is(U == class))
    {
        if (b is null) return a is null;
        if (a is null) return b is null;
    }
    else
    {
        enforce(a !is null);
    }
    return a.opEquals(b);
}

This hoists the identity test outside the opEquals call and also deals
with null references. What do you think?


Andrei

What about interfaces?

Good question! What do they do now? I ran this:

interface A {}
class Widget : A {}

void main() {
    auto a = cast(A) new Widget;
    A b = null;
    writeln(a == b);
    writeln(b == a);
}

To my surprise, the program printed false twice. If I replace A with 
Widget inside main, the program prints false then crashes with the 
mythical segfault :o).

So how are interfaces compared?


Andrei