A fresh look at comparisons

[Steven Schveighoffer]

"Janice Caron" wrote
> On 16/04/2008, Steven Schveighoffer wrote:
>>  IMO, opCmp should be
>>  defined in an interface, and those classes which implement it should
>>  implement that interface.  This would prevent trying to compare 
>> something
>>  that doesn't implement the opCmp method.
>
> Of course, you realise that just because you declare "MyClass
> implements opCmp()", it doesn't necessarily follow that all possible
> subclasses of MyClass, which may be declared by other programmers, in
> other modules, at any time in the future, will also implement opCmp().
> Nor can you be sure that your opCmp() function will be appropriate for
> all such subclasses.

Yes, but then there is no 'default' opCmp which does the wrong thing in all 
cases :)

If a derived class does not implement opCmp, it is the derived class' fault 
for saying "I'm OK with my parent's opCmp", when it actually isn't.  Not 
overriding opCmp if defined by a parent class is an unambiguous choice, 
which fits in with the standard virtual function implementation.  However, 
in the current version, nobody should EVER use the default opCmp because it 
simply isn't correct.

I'm not sure that the idea that opCmp should be a virtual function is bad or 
good.  All I'm saying is that it probably doesn't belong in Object.

-Steve