Re: [RFC] Comparable: the revenge

On Thu, Feb 19, 2015 at 10:40 PM, Adam Harvey <aharvey@php.net> wrote: > Hi all, > > Those of you with long memories will remember that I proposed a > Comparable interface way back in the pre-5.4 days, but withdrew it > when it became obvious that there was no consensus for it as a feature > and that a vote was likely to fail. > > RFC: https://wiki.php.net/rfc/comparable > PR: https://github.com/php/php-src/pull/1097 > > Why reanimate it now, I hear you ask? I think that comparisons have > only become more prominent in the language: we now have a spaceship > operator for explicit comparisons, yet the behaviour of object > comparisons can be obscure, to say the least, and the user has no > control over how their objects are compared. > > At this stage, I intend to put this up for a vote on March 5 (vote > ending March 12), with the obvious endgame being that this would be > included in 7.0. > Some technical notes on the RFC text: * "How it is ensured that if $a < $b then $b > $a?" The RFC claims that it is up to the developer to ensure this, however I don't think this is true. As far as I know PHP will implicitly enforce this. It would be good if you could double-check the behavior. * "If both $a and $b are objects with different compare functions, how it is determined whose function is used" Here you answer that the left operand wins. Once again I am unsure whether this is true - I'd assume that for > and >= the right operand wins. * I would appreciate a note that indicates how non-total / non-trichotomous comparisons can be implemented, namely by returning 1 irregardless of order. You can use a subset-relationship to illustrate this. * Have you considered the impact on exception-safety this may have? Did you verify that all places where compare_function (or derivatives) are used are exception-safe? Nikita