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.
Beispiel #1 Structure of a match
expression
<?php
$return_value = match (subject_expression) {
single_conditional_expression => return_expression,
conditional_expression1, conditional_expression2 => return_expression,
};
?>
Beispiel #2 Basic match
usage
<?php
$food = 'cake';
$return_value = match ($food) {
'apple' => 'This food is an apple',
'bar' => 'This food is a bar',
'cake' => 'This food is a cake',
};
var_dump($return_value);
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
string(19) "This food is a cake"
Hinweis: The result of a
match
expression does not need to be used.
Hinweis: 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 wayswitch
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() => ..., // $this->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(),
};
?>
Hinweis: 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.
Beispiel #3 Example of an unhandled match expression
<?php
$condition = 5;
try {
match ($condition) {
1, 2 => foo(),
3, 4 => bar(),
};
} catch (\UnhandledMatchError $e) {
var_dump($e);
}
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
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.
Beispiel #4 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);
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
string(11) "young adult"
Beispiel #5 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);
?>
Das oben gezeigte Beispiel erzeugt folgende Ausgabe:
string(2) "fr"