match

(PHP 8)

The match expression branches evaluation based on an identity check of a value. Similarly to a switch statement, a match expression has a subject expression that is compared against multiple alternatives. Unlike switch, it will evaluate to a value much like ternary expressions. Unlike switch, the comparison is an identity check (===) rather than a weak equality check (==). Match expressions are available as of PHP 8.0.0.

示例 #1 Structure of a match expression


<?php
$return_value = match (subject_expression) {
    single_conditional_expression => return_expression,
    conditional_expression1, conditional_expression2 => return_expression,
};
?>

注意: The result of a match expression does not need to be used.

注意: A match expression must be terminated by a semicolon ;.

The match expression is similar to a switch statement but has some key differences:

A match arm compares values strictly (===) instead of loosely as the switch statement does.
A match expression returns a value.
Match arms do not fall-through to later cases the way switch statements do.
A match expression must be exhaustive.

As switch statements, match expressions are executed match arm by match arm. In the beginning, no code is executed. The conditional expressions are only evaluated if all previous conditional expressions failed to match the subject expression. Only the return expression corresponding to the matching conditional expression will be evaluated. For example:


<?php
$result = match ($x) {
    foo() => ...,
    $this->bar() => ..., // bar() isn't called if foo() === $x
    $this->baz => beep(), // beep() isn't called unless $x === $this->baz
    // etc.
};
?>

match expression arms may contain multiple expressions separated by a comma. That is a logical OR, and is a short-hand for multiple match arms with the same right-hand side.


<?php
$result = match ($x) {
    // This match arm:
    $a, $b, $c => 5,
    // Is equivalent to these three match arms:
    $a => 5,
    $b => 5,
    $c => 5,
};
?>

A special case is the default pattern. This pattern matches anything that wasn't previously matched. For example:


<?php
$expressionResult = match ($condition) {
    1, 2 => foo(),
    3, 4 => bar(),
    default => baz(),
};
?>

注意: Multiple default patterns will raise a E_FATAL_ERROR error.

A match expression must be exhaustive. If the subject expression is not handled by any match arm an UnhandledMatchError is thrown.

示例 #2 Example of an unhandled match expression


<?php
$condition = 5;

try {
    match ($condition) {
        1, 2 => foo(),
        3, 4 => bar(),
    };
} catch (\UnhandledMatchError $e) {
    var_dump($e);
}
?>

以上例程会输出：

object(UnhandledMatchError)#1 (7) {
  ["message":protected]=>
  string(33) "Unhandled match value of type int"
  ["string":"Error":private]=>
  string(0) ""
  ["code":protected]=>
  int(0)
  ["file":protected]=>
  string(9) "/in/ICgGK"
  ["line":protected]=>
  int(6)
  ["trace":"Error":private]=>
  array(0) {
  }
  ["previous":"Error":private]=>
  NULL
}

Using match expressions to handle non identity checks

It is possible to use a match expression to handle non-identity conditional cases by using true as the subject expression.

示例 #3 Using a generalized match expressions to branch on integer ranges


<?php

$age = 23;

$result = match (true) {
    $age >= 65 => 'senior',
    $age >= 25 => 'adult',
    $age >= 18 => 'young adult',
    default => 'kid',
};

var_dump($result);
?>

以上例程会输出：

string(11) "young adult"

示例 #4 Using a generalized match expressions to branch on string content


<?php

$text = 'Bienvenue chez nous';

$result = match (true) {
    str_contains($text, 'Welcome') || str_contains($text, 'Hello') => 'en',
    str_contains($text, 'Bienvenue') || str_contains($text, 'Bonjour') => 'fr',
    // ...
};

var_dump($result);
?>

以上例程会输出：

string(2) "fr"