Closure::bindTo

(PHP 5 >= 5.4.0, PHP 7)

复制当前闭包对象，绑定指定的$this对象和类作用域。

说明

publicClosure::bindTo(object $newthis[,mixed $newscope= 'static']): Closure

创建并返回一个匿名函数，它与当前对象的函数体相同、绑定了同样变量，但可以绑定不同的对象，也可以绑定新的类作用域。

“绑定的对象”决定了函数体中的$this的取值，“类作用域”代表一个类型、决定在这个匿名函数中能够调用哪些私有和保护的方法。也就是说，此时$this 可以调用的方法，与$newscope类的成员函数是相同的。

静态闭包不能有绑定的对象（$newthis参数的值应该设为NULL）不过仍然可以用 bubdTo 方法来改变它们的类作用域。

This function will ensure that for a non-static closure, having a bound instance will imply being scoped and vice-versa. To this end, non-static closures that are given a scope but a NULL instance are made static and non-static non-scoped closures that are given a non-null instance are scoped to an unspecified class.

Note:
如果你只是想要复制一个匿名函数，可以用cloning代替。

参数

$newthis: 绑定给匿名函数的一个对象，或者NULL来取消绑定。
$newscope: 关联到匿名函数的类作用域，或者'static'保持当前状态。如果是一个对象，则使用这个对象的类型为心得类作用域。这会决定绑定的对象的保护、私有成员方法的可见性。

返回值

返回新创建的Closure对象或者在失败时返回FALSE

范例

Example #1 Closure::bindTo()实例

<?php
class A {
    function __construct($val) {
        $this->val = $val;
    }
    function getClosure() {
        //returns closure bound to this object and scope
        return function() { return $this->val; };
    }
}
$ob1 = new A(1);
$ob2 = new A(2);
$cl = $ob1->getClosure();
echo $cl(), "\n";
$cl = $cl->bindTo($ob2);
echo $cl(), "\n";
?>

以上例程的输出类似于：

1
2

参见

匿名函数
Closure::bind() 复制一个闭包，绑定指定的$this对象和类作用域。

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();
?>

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>

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

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
?>

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) {
}
*/
?>

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.

Closures can rebind their $this variable, but private/protected methods and functions of $this are not accessible to the closures. 
<?php
$fn = function(){
  return $this->foo;
};
class Bar{
  private $foo = 3;
}
$bar = new Bar();
$fn = $fn->bindTo($bar);
echo $fn(); // Fatal error: Cannot access private property Bar::$foo