rfc:closure_apply

PHP RFC: Closure::call

  • Version: 0.3
  • Date: 2014-07-29, put to internals 2014-08-03, latest 2014-08-19
  • Author: Andrea Faulds, ajf@ajf.me
  • Status: Accepted

Introduction

PHP has had Closures since 5.3, and since 5.4 has had Closure::bind (static method) and Closure::bindTo (method) to allow creating new closures that have $this bound to a specific method. However, it has not been possible to bind at call-time, and you must instead create a temporary new closure, making calling bound to multiple objects cumbersome and inefficient (at least two statements are needed, and a new closure must be created and immediately disposed of for each).

Proposal

A new method is added to Closure, with the following signature:

mixed Closure::call(object $to[, mixed ...$parameters])

It calls the closure with the given parameters and returns the result, with $this bound to the given object $to, using the scope of the given object. Like the bind(To) methods, a static class cannot be bound (using →call will fail).

It can be used like so:

$foo = new StdClass;
$foo->bar = 3;
$foobar = function ($qux) { var_dump($this->bar + $qux); };
$foobar->call($foo, 4); // prints int(7)

The →call method, unlike bind(To), does not take a scope parameter. Instead, it will always use the class of the object as its scope. Thus:

class Foo { private $x = 3; }
$foo = new Foo;
$foobar = function () { var_dump($this->x); };
$foobar->call($foo); // prints int(3)

call would be useful in many cases where bindTo is used (e.g. search of GitHub for bindTo). A search on GitHub reveals many using bindTo and immediately calling with call_user_func, which would now not be necessary as they could just use call.

Performance

While not the sole benefit of this RFC, it can provide a performance improvement in some applications.

We use two test scripts, a.php using bindTo and b.php using call.

a.php
$a = function () {
    return $this->x;
};
class FooBar {
    private $x = 3;
}
$foobar = new FooBar;
for ($i = 0; $i < 1000000; $i++) {
    $x = $a->bindTo($foobar, "FooBar");
    $x();
}
b.php
$a = function () {
    return $this->x;
};
class FooBar {
    private $x = 3;
}
$foobar = new FooBar;
for ($i = 0; $i < 1000000; $i++) {
    $a->call($foobar);
}

b.php shows a 2.18x improvement over a.php:

andreas-air:php-src ajf$ time sapi/cli/php a.php

real	0m1.877s
user	0m1.835s
sys	0m0.025s

andreas-air:php-src ajf$ time sapi/cli/php b.php

real	0m0.859s
user	0m0.826s
sys	0m0.018s

Backward Incompatible Changes and RFC Impact

This has no effect on backwards compatibility.

Proposed PHP Version(s)

This is proposed for the next version of PHP, either the next 5.x or PHP NEXT, whichever comes sooner. The patch is based on master, intended for PHP 7.

Future Scope

Partial application (where a new closure is returned that pre-fills the first X arguments) is a possibly worthwhile (though more difficult to implement) addition.

Vote

This is not a language change, so a straight 50%+1 Yes/No vote can be held.

Voting started 2014-08-17 but was cancelled the same day due to the removal of unbound scoped closures.

Voting started again on 2014-08-20 and ended 2014-08-27.

Closure::apply() (Approve RFC and merge into master?)
Real name Yes No
aharvey (aharvey)  
ajf (ajf)  
bishop (bishop)  
daverandom (daverandom)  
dm (dm)  
dragoonis (dragoonis)  
guilhermeblanco (guilhermeblanco)  
irker (irker)  
jedibc (jedibc)  
kalle (kalle)  
kriscraig (kriscraig)  
rdlowrey (rdlowrey)  
weierophinney (weierophinney)  
Final result: 13 0
This poll has been closed.

Patches and Tests

A branch which implements this (with a test) based on the current master can be found here: https://github.com/TazeTSchnitzel/php-src/tree/Closure_apply

There is a pull request for review purposes here: https://github.com/php/php-src/pull/775

References

Changelog

  • v0.3 - Removed unbound scoped closures, made →call use class of object as its scope
  • v0.2.1 - Added performance section
  • v0.2 - Closure::apply renamed to Closure::call for consistency with JavaScript (former takes an array in JS à la call_user_func_array, latter bare parameters)
  • v0.1 - Initial version
rfc/closure_apply.txt · Last modified: 2014/08/27 03:08 by ajf