Hi,
what about overloading operators for OBJECTs?
They do not conflict with any default operators.
I expected this to work, but it did not compile:
type generic TXQHashset<TKey, TInfo> = object //(specialize
TXQBaseHashmap<TKey,TXQVoid,TInfo>)...
class operator =(const a, b: TXQHashset): boolean;
end;
Cheers,
Benito
On 17.04.21 22:12, Jonas Maebe via fpc-devel wrote:
On 2021-04-17 22:02, Ryan Joseph via fpc-devel wrote:
Since I'm working on generics right now can we finally, at the very
least, allow class operators for comparison operators? This is
literally the only way for a generic class to override the = operator
(along with some others) so there's no reason not to allow this. I
understand the objection to :=, + etc.. where it returns a copy of a
class instance and people could in theory do memory unsafe things,
with comparison operators there is no possibility for this. I already
made a patch for "advanced records" which is in limbo but It's trivial
to adapt this for classes and put restrictions on the type of
operator.
The issue with allowing it for classes (generic or not) is that the
the = operator already has a meaning for them (pointer equality). I
think in general we don't allow overloading operators that have a
built-in meaning.
It would work very well either, because if you'd pass such a class
instance as a TObject parameter and that called routine performs a
comparison, then suddenly the comparison would happen again based on
pointer equality rather than with this custom operator. This means
that e.g. any non-generic container class that uses comparisons (for
sorting or for detecting duplicates) would fail to work, or at least
work differently than generic container classes. That's something you
don't want at all in a programming language, as it means you
constantly have to keep in mind how something you call was implemented
to know how it will behave (the called routine may even have your
class type as parameter type, but then call something else that uses
TObject).
Jonas
_______________________________________________
fpc-devel maillist - fpc-devel@lists.freepascal.org
https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
_______________________________________________
fpc-devel maillist - fpc-devel@lists.freepascal.org
https://lists.freepascal.org/cgi-bin/mailman/listinfo/fpc-devel
