Closure::fromCallable

(PHP 7 >= 7.1.0)

Closure::fromCallable — 将 callable 转换为闭包

说明

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

使用当前范围从给定的 callback 创建并返回一个新的匿名函数。此方法检查 callback 函数在作用域是否可调用，如果不能，就抛出 TypeError。

参数

callback: 要转换的回调。

返回值

返回新创建的 Closure，或者如果 callback 在当前作用域无法调用，则抛出 TypeError。

User Contributed Notes

nakerlund at gmail dot com 23-May-2018 07:20


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

?>

4-lom at live dot de 09-May-2018 01:16


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());

        };

    }

}

igorchernin at yahoo dot com 07-May-2017 08:13


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;