On 12.12.2018 at 17:28, Levi Morrison wrote: > On Wed, Dec 12, 2018 at 4:25 AM Christoph M. Becker <cmbecke...@gmx.de> wrote: >> >> On 11.12.2018 at 21:34, Levi Morrison wrote: >> >>> On Mon, Nov 26, 2018 at 2:25 PM Levi Morrison <le...@php.net> wrote: >>> >>>> I am happy to announce my latest RFC, [Covariant Returns and >>>> Contravariant Parameters][1], is open for discussion. If you do not >>>> recognize those terms then hopefully the introduction coupled with the >>>> [examples][2] will help. […] >>>> >>>> [1]: >>>> https://wiki.php.net/rfc/covariant-returns-and-contravariant-parameters >>>> [2]: >>>> https://wiki.php.net/rfc/covariant-returns-and-contravariant-parameters#examples >>> >>> It has been two weeks now. If you want to provide any feedback, or >>> follow-up on anything from the discussion, please do so soon. I hope >>> to put this to vote before the end of the year. >> >> Thanks for working on this, Levi. Highly appreciated! >> >> I may have missed this, but otherwise I'd be quite surprised that nobody >> had commented on: >> >> | Therefore, by-reference parameters are still contravariant, […] >> >> Call-by-reference is not seldom used to provide out-parameters, but >> these should not be contravariant according to LSP. Therefore, it might >> be best to keep by-reference parameters invariant. > > Christoph, we cannot make any guarantees about the type of the > variable when the function returns because the type of the parameter > is only checked on function entry, and not also on function exit, e.g. > > function array_baz(array &$in) { > $in = 1; > } > $array = []; > array_baz($array); // valid > var_export($array); // 1 > > I do think we ought to have "out" parameters some day which would > prevent this behavior (as well as have some other benefits), but that > is out of scope for this RFC. The RFC notes that if we had "inout" > parameters that they would need to be invariant. It also says that > "out" parameters would be invariant, but they may be covariant > depending on the exact semantics specified -- all that can be handled > in the RFC that proposes it.
I was not aware of this – thanks for the explanation. In my opinion, yet another good reason to avoid references. > I will add this example (or maybe a better one) to the RFC. Thanks for > bringing it up. Thanks. Also documented now: <http://svn.php.net/viewvc?view=revision&revision=346309>. -- Christoph M. Becker -- PHP Internals - PHP Runtime Development Mailing List To unsubscribe, visit: http://www.php.net/unsub.php
