PHP無名関数（クロージャ）の$thisをあとからかきかえるやつ

jabai.php

<?php
class world {
    public $v;

    public function main(){
        $this->v = 'じゃばい';

        $f = function(){
            echo $this->v;
        };

        $f();
    }
}

$world = new World;
$world->main();

wtf.php

<?php
class Box {
    public $v;
    public function __construct($str){
        $this->v = $str;
    }
    public function __invoke(){
        return function(){
            echo $this->v;
        };
    }
}

$b = new Box('Yeah!'.PHP_EOL);
$f = $b(); // make Object related closure
$f(); // => yeah!

$f = $f->bindTo(new Box('Damn!'.PHP_EOL));
$f();// => Damn!