On Tue, Jun 17, 2008 at 4:45 PM, Karoly Negyesi
Hi,
The PHP community is discussing the adding of closures and lambdas to the language, see the proposal at http://wiki.php.net/rfc/closures
If someone with knowledge of both languages could take a quick look it would be great.
Thanks a lot
Karoly Negyesi
Ps. I am not a member of the PHP internals team, I am just a PHP developer but I am very very interested in getting these in my favourite language.
Whew. Well I suspect you weren't expecting that kind of reaction. Or maybe you were... I used to be a Perl developer, and it didn't take long before I got a level 12 resistence to flame... Anyway, the proposal looks mostly okay. I don't know that much PHP, but I find the "lexical" keyword to be a nuisance. What are the semantics if the lexical keyword is omitted? (i.e. does the variable become function-local, global, what?) If it is consistent with the rest of the language, it'll do. There is a much more important point with closures: their implementation cannot be half-assed! I'm not claiming that the patch is--I have not reviewed it--but there is nothing worse than coming up with a design that relies on a language feature you only later find out has been nerfed in some way. Story of my life in C#. And nerfed closures are especially bad, because it's so hard to predict the code path. What I mean by this is the following must all be supported: * A closure must only keep alive the varables it references, not the whole pad on which they are allocated (Python messed up here) * A closure must be able to call itself recursively (via a higher-order function typically) (Squeak messed up here IIRC) * Multiple references to the same body of code with different bindings must be able to exist at the same time (duh, that's kinda what makes it a closure) * Closures must be nestable. Looking over the "Zend internal perspective" section, it looks like that implementation will mostly work. There are a couple of red flags, though: * I would recommend only saving $this in the op_array structure if the closure actually references $this -- if that is possible to deduce at the time. Otherwise you might run into unexpected poor memory performances in certain cases. (This kind of thing can make an *asymptotic* difference in memory performance; i.e. bringing the memory usage of an algorithm from O(1) to O(n), for example) * I'm worried that nested closures do not work properly with this implementation sketch. Here's a test case: $f = function ($y) { return function ($z) { return $y + $z; } }; $f(1)(2) # should give 3 And congratulations, PHP, for adopting a most essential and powerful feature! Luke