Re: [RFC] User-defined object comparison

Hi! > In other words, $a == $b must not work if $a->__equals and $b->__equals are > two different functions > > So effectively it means we only call __equals if both sides are instances > of the same class? We can just define that == calls __equals on the left. That's, for example, what Python does. This would produce a weird consequence of $a == $b and $b == $a not being the same, but that's what you get for overloading operators. That's why overloading operators is not always the best idea, because of disconnect between perceived semantics (math equality operator, which is symmetric, reflexive and transitive) and actual semantic (which is not guaranteed to have any of the math equality properties). In any case, "the same class" would be too restrictive, as there's inheritance, so we should support LSP. But then again, if $a and $b are in different places on inheritance hierarchy, we can can non-symmetric operator. This is kinda deep problem that is not really working well in most Java code, for example. See: https://www.artima.com/pins1ed/object-equality.html (for reference, Martin Odersky is the guy who did Java generics, and designed Scala, so he knows a quite bit about OO things :) -- Stas Malyshev smalyshev@gmail.com