Closure::bindTo

We can use the concept of bindTo to write a very small Template Engine:

#############
index.php
############

<?php

class Article{
    private $title = "This is an article";
}

class Post{
    private $title = "This is a post";
}

class Template{

    function render($context, $tpl){

        $closure = function($tpl){
            ob_start();
            include $tpl;
            return ob_end_flush();
        };

        $closure = $closure->bindTo($context, $context);
        $closure($tpl);

    }

}

$art = new Article();
$post = new Post();
$template = new Template();

$template->render($art, 'tpl.php');
$template->render($post, 'tpl.php');
?>

#############
tpl.php
############
<h1><?php echo $this->title;?></h1>

You can do pretty Javascript-like things with objects using closure binding:

<?php
trait DynamicDefinition {
    
    public function __call($name, $args) {
        if (is_callable($this->$name)) {
            return call_user_func($this->$name, $args);
        }
        else {
            throw new \RuntimeException("Method {$name} does not exist");
        }
    }
    
    public function __set($name, $value) {
        $this->$name = is_callable($value)? 
            $value->bindTo($this, $this): 
            $value;
    }
}

class Foo {
    use DynamicDefinition;
    private $privateValue = 'I am private';
}

$foo = new Foo;
$foo->bar = function() {
    return $this->privateValue;
};

// prints 'I am private'
print $foo->bar();

?>

Private/protected members are accessible if you set the "newscope" argument (as the manual says).

<?php
$fn = function(){
    return ++$this->foo; // increase the value
};

class Bar{
    private $foo = 1; // initial value
}

$bar = new Bar();

$fn1 = $fn->bindTo($bar, 'Bar'); // specify class name
$fn2 = $fn->bindTo($bar,  $bar); // or object

echo $fn1(); // 2
echo $fn2(); // 3

If you want to unbind completely the closure and the scope you need to set both to null:

<?php
class MyClass
{
    public $foo = 'a';
    protected $bar = 'b';
    private $baz = 'c';

    /**
     * @return array
     */
    public function toArray()
    {
        // Only public variables
        return (function ($obj) {
            return get_object_vars($obj);
        })->bindTo(null, null)($this);
    }
}
?>

In this example, only the public variables of the class are exported (foo).

If you use the default scope (->bindTo(null)) also protected and private variables are exported (foo, bar and baz).

It was hard to figure it out because there is nowhere mentioned in the documentation that you can use null as a scope.

Access private members of parent classes; playing with the scopes:
<?PHP
class Grandparents{ private $__status1 = 'married'; }
class Parents extends Grandparents{ private $__status2 = 'divorced'; }
class Me extends Parents{ private $__status3 = 'single'; }

$status1_3 = function()
{
    $this->__status1 = 'happy';
    $this->__status2 = 'happy';
    $this->__status3 = 'happy';
};

$status1_2 = function()
{
    $this->__status1 = 'happy';
    $this->__status2 = 'happy';
};

// test 1:
$c = $status1_3->bindTo($R = new Me, Parents::class);            
#$c();    // Fatal: Cannot access private property Me::$__status3

// test 2:
$d = $status1_2->bindTo($R = new Me, Parents::class);
$d();
var_dump($R);
/*
object(Me)#5 (4) {
  ["__status3":"Me":private]=>
  string(6) "single"
  ["__status2":"Parents":private]=>
  string(5) "happy"
  ["__status1":"Grandparents":private]=>
  string(7) "married"
  ["__status1"]=>
  string(5) "happy"
}
*/

// test 3:
$e = $status1_3->bindTo($R = new Me, Grandparents::class);    
#$e(); // Fatal: Cannot access private property Me::$__status3

// test 4:
$f = $status1_2->bindTo($R = new Me, Grandparents::class);    
$f();
var_dump($R);
/*
object(Me)#9 (4) {
  ["__status3":"Me":private]=>
  string(6) "single"
  ["__status2":"Parents":private]=>
  string(8) "divorced"
  ["__status1":"Grandparents":private]=>
  string(5) "happy"
  ["__status2"]=>
  string(5) "happy"
}
*/
?>

Clear the stack trace:
<?PHP
use Exception;
use ReflectionException;

$c = function()
{
    $this->trace = [];
};

$c = $c->bindTo($R = new ReflectionException, Exception::class);
$c();

try
{
    throw $R;
}
catch(ReflectionException $R)
{
    var_dump($R->getTrace());
}
/*
array(0) {
}
*/
?>

With rebindable $this at hand it's possible to do evil stuff:

<?php
    class A {
        private $a = 12;
        private function getA () {
            return $this->a;
        }
    }
    class B {
        private $b = 34;
        private function getB () {
            return $this->b;
        }
    }
    $a = new A();
    $b = new B();
    $c = function () {
        if (property_exists($this, "a") && method_exists($this, "getA")) {
            $this->a++;
            return $this->getA();
        }
        if (property_exists($this, "b") && method_exists($this, "getB")) {
            $this->b++;
            return $this->getB();
        }
    };
    $ca = $c->bindTo($a, $a);
    $cb = $c->bindTo($b, $b);
    echo $ca(), "\n"; // => 13
    echo $cb(), "\n"; // => 35
?>

If you, like me, did not immediately understand what exactly "(an object of) an internal class" in the documentation about the 'newScope' parameter:

By an internal class, the documentation means any internal PHP class such as 'stdClass', 'Closure', 'WeakMap', and etc:

<?php

class A {}
$a = new A();
$closure = fn() => null;

$binded = $closure->bindTo($a, 'stdClass',); // Cannot bind closure to scope of internal class stdClass
$binded = $closure->bindTo($a, $closure,); // Warning: Cannot bind closure to scope of internal class Closure etc.

Get all object vars without using Reflection:

<?php

declare(strict_types=1);

class A
{
    private $foo = 'foo';
    protected $bar = 'bar';
    public $buz = 'buz';
}

function get_object_vars_all($object): array
{
    if (!\is_object($object)) {
        throw new \InvalidArgumentException(sprintf('The argument should be an object, "%s" given.', get_debug_type($object)));
    }

    $closure = function () {
        return get_object_vars($this);
    };

    return $closure->bindTo($object, $object)();
}

$a = new A();

var_dump(get_object_vars($a));
var_dump(get_object_vars_all($a));

?>

The output: 

array(1) {
  ["buz"]=>
  string(3) "buz"
}
array(3) {
  ["foo"]=>
  string(3) "foo"
  ["bar"]=>
  string(3) "bar"
  ["buz"]=>
  string(3) "buz"
}