Closure::fromCallable

(PHP 7 >= 7.1.0)

Closure::fromCallable — Convierte un 'callable' en un cierre

Descripción

public static Closure::fromCallable(callable $callback): Closure

Crea y devuelve una nueva función anónima desde el callback dado empleando el ámbito actual. Este método comprueba si callback es llamable en el ámbito actual, lanzando un TypeError si no lo es.

Nota:
A partir de PHP 8.1.0, Sintaxis de llamada de primera clase tiene la misma semántica que este método.

Parámetros

callback: El «callable» a convertir.

Valores devueltos

Devuelve el recién creado Closure o lanza un TypeError si callback no es llamable en el ámbito actual.

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User Contributed Notes 3 notes

down

igorchernin at yahoo dot com ¶

7 years ago

It seems that the result of the "fromCallable" behaves a little bit different then an original Lambda function.

class A {
    private $name;
    public function __construct($name)
    {
        $this->name = $name;
    }
}

// test callable
function getName()
{
      return $this->name;
}
$bob = new A("Bob");

$cl1 = Closure::fromCallable("getName");
$cl1 = $cl1->bindTo($bob, 'A');

//This will retrieve: Uncaught Error: Cannot access private property A::$name 
$result = $cl1();
echo $result;

//But for a Lambda function
$cl2 = function() {
    return $this->name;
};
$cl2 = $cl2->bindTo($bob, 'A');
$result = $cl2();

// This will print Bob
echo $result;

down

4-lom at live dot de ¶

6 years ago

Sadly, your comparison is incorrect.

// The equivalent to
$cl1 = Closure::fromCallable("getName");
$cl1 = $cl1->bindTo($bob, 'A');

// is most likely this
$cl2 = function() {
    return call_user_func_array("getName", func_get_args());
};
$cl2 = $cl2->bindTo($bob, 'A');

Executing one or the other Closure should result in the same access violation error you already postet.

----
A simple PHP 7.0 polyfill could look like this:
----

namespace YourPackage;

/**
 * Class Closure
 *
 * @see \Closure
 */
class Closure
{
    /**
     * @see \Closure::fromCallable()
     * @param callable $callable
     * @return \Closure
     */
    public static function fromCallable(callable $callable)
    {
        // In case we've got it native, let's use that native one!
        if(method_exists(\Closure::class, 'fromCallable')) {
            return \Closure::fromCallable($callable);
        }

        return function () use ($callable) {
            return call_user_func_array($callable, func_get_args());
        };
    }
}

down

nakerlund at gmail dot com ¶

6 years ago

I have two points:

It is possible to use Closure::fromCallable to convert private/protected methods to closures and use them outside the class.

Closure::fromCallable accepts late dynamic bindings using the keyword static if provided as a string. 

My code below demonstrate how a private static method can be used as a callback in a function outside the class.

<?php
function myCustomMapper ( Callable $callable, string $str ): string {
  return join(' ', array_map( $callable, explode(' ', $str) ) );
}

class MyClass {

    public static function mapUCFirst ( string $str ): string {
        $privateMethod = 'static::mapper';
        $mapper = Closure::fromCallable( $privateMethod );
        return myCustomMapper( $mapper, $str );
    }
    private static function mapper ( string $str ): string {
        return ucfirst( $str );
    }

}

echo MyClass::mapUCFirst('four little uncapitalized words');
// Prints: Four Little Uncapitalized Words
?>

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