What is the purpose of the "use" command and what is its relation to anonymous functions?

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What is the purpose of the "use" command and what is its relation to anonymous functions?

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#1 by (8 votes)

10

I'm doing tests with a RESTFul API that I'm creating using the Slim micro-framework, and in one of those routines that is responsible for executing a particular action, I was struck by a command I did not know, which is the command use .

Below is an example of the command use in a method that returns a JSON with the data obtained from the database:

//Listando todas pessoas
$app->get('/pessoas/', 
        function() use ($app) 
        {
            (new \controllers\Pessoa($app))->listar();            
        });

This command seems to be part of the anonymous function function() that is responsible for the route:

http://localhost/RestApiEx/pessoas/

And the use of it left me with the following doubts.

Questions

I would like to know what is the purpose of the use command and what is the relation it has with anonymous functions?

php

asked by anonymous 18.12.2016 / 01:40

1 answer

Function as parameter in functions in jQuery Circle with curved edge

score 8 · Accepted Answer

The use passes the value of one or more variables to the scope of the anonymous function making this value accessible (inheriting the variable), for example if you do this:

<?php

$a = 'Olá, mundo!';

$foo = function() {
   echo $a;
};

$foo();

You will acknowledge that the variable has not been defined, something like:

PHP Notice: Undefined variable: a in example.php on line 6

But if you do this:

<?php

$a = 'Olá, mundo!';

$foo = function() use ($a) {
   echo $a;
};

$foo();

It will print the value 'Olá, mundo!'

In the Slim framework the main application variable is $app , but to make it accessible to the scope of the anonymous function, use is required, if you do this:

$app->get('/pessoas/', 
        function() 
        {
            (new \controllers\Pessoa($app))->listar();            
        });

You would have a similar error:

PHP Notice: Undefined variable: app in example.php on line 9

And your controller would get a value null instead of the object new \Slim\App;

Doc: link

Extras

One detail, while using use , the example% variable is not a reference , if you do something like this:

<?php

$a = 1;

$foo = function() use ($a) {
   $a += 10;
};

$foo();

echo $a;

It will be displayed:

1

But if you refer:

<?php

$a = 1;

$foo = function() use (&$a) {
   $a += 10;
};

$foo();

echo $a;

11 will be displayed:

11

Something important to note is that in PHP there is another $a , which is used to create class aliases, like this:

<?php

use Foo\Bar\Baz; //é possivel chamar new Baz, sem o namespace completo
use Foo\Bar\Baz as Test; //é possivel chamar new Test para se referir ao Foo\Bar\Baz