`__invoke` vs `function` vs `Closure`

__invoke.php

<?php

final class Login
{
    private $sessions;
    
    public function __construct(SessionRepository $sessions)
    {
        $this->sessions = $sessions;
    }
    
    public function __invoke(User $user)
    {
        $session = new Session($user);
        
        $this->sessions->add($session);
        
        return $session;
    }
}

// usage (PHP 7) - see http://3v4l.org/kPnLM:

$session = (new Login($sessionRepository))($user);

README.md

__invoke VS function VS Closure

This gist is about:

• https://twitter.com/taylorotwell/status/600680897550098432
• https://twitter.com/Ocramius/status/600705252539691008

Mainly:

• function cannot (should not) be used when side-effects occur
• function does not work with dependency injection
• function is not testable in isolation if it isn't a pure function without dependencies

In order to fix the problems exposed above, and avoid global or static scope pollution, two approaches are possible:

• using a Closure, combined with a higher order function (also called functor)
• using an object that implements the __invoke magic method

Few notes:

• a class that only implements __invoke and __construct is basically a function combined with a functor

• a class can be easily tested in isolation

• a Closure with dependencies cannot be tested in isolation

• in order to make a Closure testable in isolation, it must be combined with a higher order function

• there is no runtime difference between using a Closure and any object with an __invoke method defined in its class

• in PHP, $a = function () use (...) {} simply means "call the constructor of class Closure with these parameters and this body for __invoke", so you end up with an object that implements __invoke anyway.

Therefore, object + __invoke is much simpler and flexible than using a Closure, whereas a function is not applicable in any context that requires the usage of DI.

closure.php

<?php

// higher order function / factory - you name it
$loginFactory = function (SessionRepository $sessions) {

    return function (User $user) use ($sessions) {
        // argh! (note that a static registry/locator isn't any better)
        global $sessions;
        
        $session = new Session($user);
            
        $sessions->add($session);
            
        return $session;
    };
};

// usage (PHP 7) - see http://3v4l.org/kPnLM:

$session = $loginFactory(sessionRepository)($user);

function.php

<?php

function login(User $user)
{
    // argh! (note that a static registry/locator isn't any better)
    global $sessions;
    
    $session = new Session($user);
        
    $sessions->add($session);
        
    return $session;
}

// usage:

$session = login($user);

Thank you for sharing knowledge and congratulations on the gist

A small adjustment that can be made in the example closure.php would be:

$session = $loginFactory(sessionRepository) ($user);

for

$session = $loginFactory($sessionRepository) ($user);