On 19/03/2013 05:38, Jonathan M Davis wrote:
<snip>
Well, IIRC, if when you override a function, and you give it a
different parameter type, it's a new overload rather than actually
overriding anything (even if the type of the parameter in the derived
type's function is a derived type of the type of the parameter in the
base class' function).
I've just been reminding myself of what
http://dlang.org/hijack.html
says about this. As it turns out, they are indeed separate overloads,
albeit protected by hiding the base class's version from derived class
references.
So, if you don't use a common type for the parameter, you'll run into
overload conflicts regardless. So, while you _could_ use something
other than Object, you could run into overload conflicts if you do.
That can be gotten around by aliasing base class functions into the
scope of the derived class (though that may cause derived types to be
compared as base types if they're referred to via references to the
base type, so that may no be a good idea) or by creating overloads
for comparing every base class, but it's arguably easier to just
accept Object and cast - or accept whatever the base type is which
first introduces opEquals into the hierarchy.
<snip>
I've always defined both opEquals(Object) and opEquals(MyClass), and
likewise for opCmp where applicable, and made the Object version call
the class-specific version. This way, the overhead of a cast is avoided
in the case where you're comparing two objects through references of the
specific class type.
Of course, once these are removed from Object, it will just be a case of
removing the Object versions of these methods from my class.
But the question still remains: How do we implement this change without
causing mass disruption? It might be the case that programmers just
need to remove opEquals(Object) and opCmp(Object) from their classes,
and remove the override attribute from toHash and toString (and declare
them const as appropriate). But there will be a lot of libraries to
convert, and it will take time for them all to be converted.
Stewart.
