(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.
Example #1 Structure of a match expression
<?php
$return_value = match (subject_expression) {
single_conditional_expression => return_expression,
conditional_expression1, conditional_expression2 => return_expression,
};
?>
Note: The result of a
matchexpression does not need to be used.
Note: A
matchexpression must be terminated by a semicolon;.
The match expression is similar to a
switch statement but has some key differences:
match arm compares values strictly (===) instead
of loosely as the switch statement does.
match expression returns a value.
match arms do not fall-through to later cases the way
switch statements do.
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(),
};
?>
Note: Multiple default patterns will raise a
E_FATAL_ERRORerror.
A match expression must be exhaustive. If the
subject expression is not handled by any match arm an
UnhandledMatchError is thrown.
Example #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
}
It is possible to use a match expression to handle
non-identity conditional cases by using true as the subject
expression.
Example #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"
Example #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"
This will allow for a nicer FizzBuzz solution:
<?php
function fizzbuzz($num) {
print match (0) {
$num % 15 => "FizzBuzz" . PHP_EOL,
$num % 3 => "Fizz" . PHP_EOL,
$num % 5 => "Buzz" . PHP_EOL,
default => $num . PHP_EOL,
};
}
for ($i = 0; $i <=100; $i++)
{
fizzbuzz($i);
}
The comment correcting Hayley's example misses that year is also present in the example, but not a function argument.
Most code from PHP.net should not be copied without user care. It was nonetheless, a great example of using short syntax to reduce complexity.
In the "familiar example" presented by Hayley Watson the following code is incorrect:
strtolower(substr($name, 0, 3))
It should instead be written in both instances as:
strtolower(substr($month, 0, 3))
As well as being similar to a switch, match expressions can be thought of as enhanced lookup tables — for when a simple array lookup isn't enough without extra handling of edge cases, but a full switch statement would be overweight.
For a familiar example, the following
<?php
function days_in_month(string $month): int
{
static $lookup = [
'jan' => 31,
'feb' => 0,
'mar' => 31,
'apr' => 30,
'may' => 31,
'jun' => 30,
'jul' => 31,
'aug' => 31,
'sep' => 30,
'oct' => 31,
'nov' => 30,
'dec' => 31
];
$name = strtolower(substr($name, 0, 3));
if(isset($lookup[$name])) {
if($name == 'feb') {
return is_leap($year) ? 29 : 28;
} else {
return $lookup[$name];
}
}
throw new InvalidArgumentException("Bogus month");
}
?>
with the fiddly stuff at the end, can be replaced by
<?php
function days_in_month(string $month): int
{
return match(strtolower(substr($name, 0, 3))) {
'jan' => 31,
'feb' => is_leap($year) ? 29 : 28,
'mar' => 31,
'apr' => 30,
'may' => 31,
'jun' => 30,
'jul' => 31,
'aug' => 31,
'sep' => 30,
'oct' => 31,
'nov' => 30,
'dec' => 31,
default => throw new InvalidArgumentException("Bogus month"),
};
}
?>
Which also takes advantage of "throw" being handled as of PHP 8.0 as an expression instead of a statement.