Closures don't work as class methods?

Question

Am I missing something or do closures simply not work as class methods? Take this for instance:

$foo = new stdClass();
$foo->bar = function() {
   echo '@@@';
};
$foo->bar();

Seems to give me an error of "Fatal error: Call to undefined method stdClass::bar() in /blah/blah.php on line X"

Shouldn't this instead invoke the closure that was placed in the "bar" property?

Christian · Accepted Answer · 2011-10-24T19:48:42.980

5

Yes, that is indeed correct.

The only way to call bar is:

$bar = $foo->bar;
$bar();

Sad, but true.

~~Also worth noting, because of this same effect, there is no $this inside $bar call (unless you pass it as function argument named as $this).~~

Edit: As nikic pointed out, the value of $this inside the closure is the same value of the scope of when the closure was created. This may mean that $this might be undefined on two occasions: when the scope was the global PHP scope or when the scope was from a static context. This, however, means that you can in theory feed the correct instance:

class Foo {
    public $prop = 'hi';
    function test(){
        $this->bar = function(){
            echo $this->prop;
        }

        $bar = $this->bar;
        $bar();
    }
}

$foo = new Foo();
$foo->test();

Also, it seems that with some class magic, you can achieve $this->bar() as well:

class Foo {
    // ... other stuff from above ...
    public function __call($name, $args){
        $closure = $this->$name;
        call_user_func_array( $closure, $args ); // *
    }
}

[*] Beware that call_user_func_array is very slow.

Oh, and this is strictly for PHP 5.4 only. Before that, there's no $this in closures :)

Also, you can see it in action here.

edited Oct 24 '11 at 19:48

answered Oct 24 '11 at 19:27

Christian

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guh. is this going to be changed anytime soon? – dqhendricks Oct 24 '11 at 19:29
$this in a closure gives me an error that it was used in a non object context even though it was defined within an object as well as called within an object. – dqhendricks Oct 24 '11 at 19:50
Are you using PHP 5.4? Please do try my demonstration on viper7. – Christian Oct 24 '11 at 20:00
@dqhendricks you're out of luck then :/ – Christian Oct 24 '11 at 20:43
It's also possible to call a closure class member using `->invoke()`. http://stackoverflow.com/questions/4535330/calling-closure-assigned-to-object-property-directly/14063179#14063179 – Brilliand Feb 28 '14 at 16:14

score 1 · Answer 2 · answered Oct 25 '11 at 09:17

1

Methods and fields are completely separate; in fact, you can even have a method and field of the same name:

<?php
class foo{
    function bar() { echo "hello\n"; }
}
$object = new foo;
$object->bar = 1;
$object->bar(); // echoes "hello"
?>

This explains why your syntax could not have created a "real" method.

answered Oct 25 '11 at 09:17

newacct

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I didn't expect it to create a "real" method, but I did expect it to let me invoke the closure within the property. – dqhendricks Oct 25 '11 at 14:33
@dqhendricks: then there would be no syntactical difference between calling the method `bar` and calling the function stored in the field `bar`. So it would be ambiguous what you were doing – newacct Nov 01 '11 at 00:05
you are correct. this would cause confusion. this would have been a very useful feature in my particular case however, but i have found a way to implement the same functionality without it. – dqhendricks Nov 01 '11 at 01:12

Closures don't work as class methods?

2 Answers2