PHP – Closure::call()

In PHP, a closure is an anonymous function that has access to the variables in the scope in which it was created, even after that scope has closed. You need to specify use keyword in it.

Closures are objects that encapsulate the function code and the scope in which they were created. With PHP 7, a new closure::call() method was introduced to bind an object scope to a closure and invoke it.

Methods in the Closure Class

The Closure class has the following methods including the call() method −

final class Closure {

   /* Methods */
   private __construct()
   public static bind(Closure $closure, ?object $newThis, object|string|null $newScope = "static"): ?Closure
   public bindTo(?object $newThis, object|string|null $newScope = "static"): ?Closure
   public call(object $newThis, mixed ...$args): mixed
   public static fromCallable(callable $callback): Closure
   
}

The call() method is a static method of Closure class. It has been introduced as a shortcut the bind() or bindTo() methods.

The bind() method Duplicates a closure with a specific bound object and class scope while the bindTo() method duplicates the closure with a new bound object and class scope.

The call() method has the following signature −

public Closure::call(object $newThis, mixed ...$args): mixed

The call() method temporarily binds the closure to newThis, and calls it with any given parameters.

With version prior to PHP 7, the bindTo() method can be used as follows −

<?php
   class A {
      private $x = 1;
   }

   // Define a closure Pre PHP 7 code
   $getValue = function() {
      return $this->x;
   };

   // Bind a clousure
   $value = $getValue->bindTo(new A, 'A'); 
   print($value());
?>

The program binds the $getValue which is a closure object, to the object of A class and prints the value of its private variable $x – it is 1.

With PHP 7, the binding is achieved by call() method as shown below −

<?php
   class A {
      private $x = 1;
   }

   // PHP 7+ code, Define
   $value = function() {
      return $this->x;
   };

   print($value->call(new A));
?>