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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.

add a note

User Contributed Notes 6 notes

up
33
InvisibleSmiley
3 years ago
Unlike anonymous functions, arrow functions cannot have a void return type declaration.

May seem obvious, but if you thought you could make use of the benefits of arrow functions (using variables from the parent scope) to simplify a function or method call, keep in mind that this is only possible if you do NOT tell PHP that the arrow function does indeed return void.
up
36
Koushil Mankali
3 years ago
In 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

?>

Here we can use reference variable in fn(&$x) and pass the value from function call $fn($x) so that we will get the output as expected with out using Anonymous functions.

Example:

<?php

$x
= 1;
$fn = fn(&$x) => $x++;
$fn($x);
var_export($x);

?>

Output : 2 (as expected)

But here it will not take values from parent scope automatically but we have to pass them explicitly.
up
18
itsunclexo at gmail dot com
2 years ago
As you already know, variable bindings occur in arrow functions by "by-value". That means, an arrow function returns a copy of the value of the variable used in it from the outer scope.

Now let us see an example of how a arrow function returns a reference instead of a copy of a value.

<?php

$x
= 0;

$fn = fn &(&$x) => $x; // Returns a reference

$y = &$fn($x); // Now $y represents the reference

var_dump($y); // Outputs: 0

$y = 3; // Changing value of $y affects $x

var_dump($x); // Ouputs: 3

?>
up
12
dexen dot devries at gmail dot com
3 years ago
Beware compact() not being able to access (import) variables from external scope (known in versions: 7.4.0, 7.4.8) (bug: https://bugs.php.net/bug.php?id=78970).

A workaround is available - use the variable directly; this will cause it to be imported into the arrow function's namespace and make it available to the compact() too.

<?php
$aa
= 111;
$accessing_variable_works = fn($bb) => [ $aa, $bb ];
$compact_is_broken = fn($bb) => compact('aa', 'bb');
$compact_can_work_with_workaround = fn($bb) => compact('aa', 'bb') + ['workaround' => $aa];
var_dump($accessing_variable_works(333));
var_dump($compact_is_broken(555));
var_dump($compact_can_work_with_workaround(777));
?>

result:
array(2) {
[0]=>
int(111)
[1]=>
int(333)
}
PHP Notice: compact(): Undefined variable: aa in /home/m/vlt/guitar/tlb/s/public_html/index.php on line 9
array(1) {
["bb"]=>
int(555)
}
array(3) {
["aa"]=>
int(111)
["bb"]=>
int(777)
["workaround"]=>
int(111)
}
up
0
cjyf-yqp at 126 dot com
9 days ago
Avariable avariables also don't work in arrow functions.
<?php
$var
= 'outer';
echo (fn(
$x)=>$$x)('var'); // Warning: Undefined variable $var
?>
up
-54
zhangchengming at kkguan dot com
3 years ago
<?php

$x
= 1;

(fn() => print(
$x))(); // Outputs 1

(fn($x) => print($x))(2); // Outputs 2
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