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));
?>
以上例程会输出：
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
?>
| 版本 | 说明 |
|---|---|
| 7.4.0 | Arrow functions became available. |
Note: It is possible to use func_num_args(), func_get_arg(), and func_get_args() from within an arrow function.