Does a PHP static anonymous function really work?

问题

I'm trying to learn PHP, and now I'm stuck in 'static anonymous function'.

I found this in a tutorial (http://www.slideshare.net/melechi/php-53-part-2-lambda-functions-closures-presentation)

"Object Orientation

Lambda Functions are Closures because they automatically get bound to the scope of the class that they are created in.

'$this' is not always needed in the scope.

Removing '$this' can save on memory.

You can block this behaviour by declaring the Lambda Function as static."

What is wrong with this code?

I get this error:

Parse error: parse error, expecting `T_PAAMAYIM_NEKUDOTAYIM' in C:\wamp\www\z-final\a.php on line 11

Why this code line doesn't work "return static function(){var_dump($this);};" ?

class foo
{
    public function getLambda()
    {
        return function(){var_dump($this);};
    }

    public function getStaticLambda()
    {
        return static function(){var_dump($this);};
    }
}

$foo = new foo();
$lambda = $foo->getLambda();
$staticLambda = $foo->getStaticLambda();
$lambda();
$staticLambda();

回答1:

Yes, that is perfectly valid syntax in 5.4+.

Basically, it prevents auto-binding of the current class to the closure (in fact, it prevents all binding, but more on that later).

class Foo {
    public function bar() {
        return static function() { var_dump($this); };
    }
    public function baz() {
        return function() { var_dump($this); };
    }
}

If we instantiate that on 5.4+, the closure bar() returns will have $this set to null. Just as if you made a static call to it. But baz() would have $this set to the foo instance you called baz() on.

So:

$bar = $f->bar();

$bar();

Results in:

Notice: Undefined variable: this in /in/Bpd3d on line 5

NULL

And

$baz = $f->baz();

$baz();

Results in

object(Foo)#1 (0) {

}

Make sense? Great.

Now, what happens if we take closures defined outside of a function:

$a = function() { var_dump($this); };
$a();

We get null (and a notice)

$c = $a->bindTo(new StdClass());
$c();

We get StdClass, just as you'd expect

$b = static function() { var_dump($this); };
$b();

We get null (and a notice)

$d = $b->bindTo(new StdClass());
$d();

This is where things get interesting. Now, we get a warning, a notice, and null:

Warning: Cannot bind an instance to a static closure in /in/h63iF on line 12

Notice: Undefined variable: this in /in/h63iF on line 9

NULL

So in 5.4+, you can declare a static closure, which results in it never getting $this bound to it, nor can you ever bind an object to it...

回答2:

There should be no need to define it with the static keyword.

<?php
class House
{
     public function paint($color)
     {
         return function() use ($color) { return "Painting the house $color..."; };
     }
}

$house = new House();
$callback = $house->paint('red');
var_dump($callback); // object(Closure)#2 (2) {..}
var_dump($callback()); // "Painting the house red..."

来源：https://stackoverflow.com/questions/12579657/does-a-php-static-anonymous-function-really-work

标签

php

anonymous-function