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Arrow Functions

Arrow functions were introduced in PHP 7.4 as a more concise syntax for anonymous functions.

Both anonymous functions and arrow functions are implemented using the Closure class.

Arrow functions have the basic form fn (argument_list) => expr.

Arrow functions support the same features as anonymous functions, except that using variables from the parent scope is always automatic.

When a variable used in the expression is defined in the parent scope it will be implicitly captured by-value. In the following example, the functions $fn1 and $fn2 behave the same way.

Example #1 Arrow functions capture variables by value automatically

<?php

$y 
1;
 
$fn1 fn($x) => $x $y;
// equivalent to using $y by value:
$fn2 = function ($x) use ($y) {
    return 
$x $y;
};

var_export($fn1(3));
?>

The above example will output:

4

This also works if the arrow functions are nested:

Example #2 Arrow functions capture variables by value automatically, even when nested

<?php

$z 
1;
$fn fn($x) => fn($y) => $x $y $z;
// Outputs 51
var_export($fn(5)(10));
?>

Similarly to anonymous functions, the arrow function syntax allows arbitrary function signatures, including parameter and return types, default values, variadics, as well as by-reference passing and returning. All of the following are valid examples of arrow functions:

Example #3 Examples of arrow functions

<?php

fn
(array $x) => $x;
static 
fn(): int => $x;
fn($x 42) => $x;
fn(&$x) => $x;
fn&($x) => $x;
fn($x, ...$rest) => $rest;

?>

Arrow functions use by-value variable binding. This is roughly equivalent to performing a use($x) for every variable $x used inside the arrow function. A by-value binding means that it is not possible to modify any values from the outer scope. Anonymous functions can be used instead for by-ref bindings.

Example #4 Values from the outer scope cannot be modified by arrow functions

<?php

$x 
1;
$fn fn() => $x++; // Has no effect
$fn();
var_export($x);  // Outputs 1

?>

Changelog

Version Description
7.4.0 Arrow functions became available.

Notes

Note: It is possible to use func_num_args(), func_get_arg(), and func_get_args() from within an arrow function.

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