php closures: why the 'static' in the anonymous function declaration when binding to static class?

Question

The example in the php documentation on Closure::bind include static on the anonymous function declaration. why? I can't find the difference if it is removed.

with:

class A {     private static $sfoo = 1; } $cl1 = static function() { // notice the "static"     return self::$sfoo; }; $bcl1 = Closure::bind($cl1, null, 'A'); echo $bcl1(); // output: 1 

without:

class A {     private static $sfoo = 1; } $cl1 = function() {     return self::$sfoo; }; $bcl1 = Closure::bind($cl1, null, 'A'); echo $bcl1(); // output: 1 

Answer 1

found the difference: you can't bind static closures to object, only change the object scope.

class foo { }  $cl = static function() { };  Closure::bind($cl, new foo); // PHP Warning:  Cannot bind an instance to a static closure Closure::bind($cl, null, 'foo') // you can change the closure scope