Php/docs/functions.arrow
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 ../class.closureClosure 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 + $z;// Outputs 51var_export($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
<?phpfn(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.