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
