International PHP Conference Munich 2024

match

(PHP 8)

match 表达式基于值的一致性进行分支计算。 match表达式和 switch 语句类似, 都有一个表达式主体,可以和多个可选项进行比较。 与 switch 不同点是,它会像三元表达式一样求值。 与 switch 另一个不同点,它的比较是严格比较( ===)而不是松散比较(==)。 Match 表达式从 PHP 8.0.0 起可用。

示例 #1 match 表达式结构

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

示例 #2 match 的基础用法

<?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);
?>

以上示例会输出:

string(19) "This food is a cake"

示例 #3 使用 match 和比较运算符的示例

<?php
$age
= 18;

$output = match (true) {
$age < 2 => "Baby",
$age < 13 => "Child",
$age <= 19 => "Teenager",
$age > 19 => "Young adult",
$age >= 40 => "Old adult"
};

var_dump($output);
?>

以上示例会输出:

string(8) "Teenager"

注意: 不一定要使用 match 表达式的结果。

注意: match 表达式必须使用分号 ; 结尾。

match 表达式跟 switch 语句相似,但是有以下关键区别:

  • match 比较分支值,使用了严格比较 (===), 而 switch 语句使用了松散比较。
  • match 表达式会返回一个值。
  • match 的分支不会像 switch 语句一样, 落空时执行下个 case。
  • match 表达式必须彻底列举所有情况。

match 表达式和 switch 语句类似, 逐个检测匹配分支。一开始不会执行代码。 只有在所有之前的条件不匹配主体表达式时,才会执行剩下的条件表达式。 只会执行返回的表达式所对应的匹配条件表达式。 举例:

<?php
$result
= match ($x) {
foo() => ...,
$this->bar() => ..., // 如果 foo() === $x,不会执行 $this->bar()
$this->baz => beep(), // 只有 $x === $this->baz 时才会执行 beep()
// 等等
};
?>

match 表达式分支可以通过逗号分隔,包含多个表达式。 这是一个逻辑 OR,当多个分支表达式右侧相同时,就可以用这种缩写。

<?php
$result
= match ($x) {
// 匹配分支:
$a, $b, $c => 5,
// 等同于以下三个分支:
$a => 5,
$b => 5,
$c => 5,
};
?>

default 模式是个特殊的条件。 当之前的条件都不匹配时,会匹配到该模式。 For example:

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

注意: 多个 default 模式将会触发 E_FATAL_ERROR 错误。

match 表达式必须详尽列出所有情况。 如果主体表达式不能被任意分支条件处理, 会抛出 UnhandledMatchError

示例 #4 match 表达式存在未处理的示例

<?php
$condition
= 5;

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

以上示例会输出:

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
}

使用 match 表达式处理非一致性检查

可以使用 match 表达式将 true 作为主项表达式来处理非一致性条件的情况。

示例 #5 针对整数范围,使用宽泛的表达式匹配分支

<?php

$age
= 23;

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

var_dump($result);
?>

以上示例会输出:

string(11) "young adult"

示例 #6 针对字符串内容,使用宽泛的表达式匹配分支

<?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);
?>

以上示例会输出:

string(2) "fr"
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User Contributed Notes 9 notes

up
81
darius dot restivan at gmail dot com
3 years ago
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);
}
up
70
Anonymous
2 years ago
<?php
function days_in_month(string $month, $year): int
{
return match(
strtolower(substr($month, 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"),
};
}
?>

can be more concisely written as

<?php
function days_in_month(string $month, $year): int
{
return match(
strtolower(substr($month, 0, 3))) {
'apr', 'jun', 'sep', 'nov' => 30,
'jan', 'mar', 'may', 'jul', 'aug', 'oct', 'dec' => 31,
'feb' => is_leap($year) ? 29 : 28,
default => throw new
InvalidArgumentException("Bogus month"),
};
}
?>
up
6
Sbastien
1 year ago
I use match instead of storing PDOStatement::rowCount() result and chaining if/elseif conditions or use the ugly switch/break :

<?php

$sql
= <<<SQL
INSERT INTO ...
ON DUPLICATE KEY UPDATE ...
SQL;

$upkeep = $pdo->prepare($sql);

$count_untouched = 0;
$count_inserted = 0;
$count_updated = 0;

foreach (
$data as $record) {
$upkeep->execute($record);
match (
$upkeep->rowCount()) {
0 => $count_untouched++,
1 => $count_inserted++,
2 => $count_updated++,
};
}

echo
"Untouched rows : {$count_untouched}\r\n";
echo
"Inserted rows : {$count_inserted}\r\n";
echo
"Updated rows : {$count_updated}\r\n";
up
54
Hayley Watson
3 years ago
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 $month): int
{
return match(
strtolower(substr($month, 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.
up
7
thomas at zuschneid dot de
1 year ago
While match allows chaining multiple conditions with ",", like:
<?php
$result
= match ($source) {
cond1, cond2 => val1,
default =>
val2
};
?>
it seems not valid to chain conditions with default, like:
<?php
$result
= match ($source) {
cond1 => val1,
cond2, default => val2
};
?>
up
9
php at joren dot dev
2 years ago
If you want to execute multiple return expressions when matching a conditional expression, you can do so by stating all return expressions inside an array.

<?php
$countries
= ['Belgium', 'Netherlands'];
$spoken_languages = [
'Dutch' => false,
'French' => false,
'German' => false,
'English' => false,
];

foreach (
$countries as $country) {
match(
$country) {
'Belgium' => [
$spoken_languages['Dutch'] = true,
$spoken_languages['French'] = true,
$spoken_languages['German'] = true,
],
'Netherlands' => $spoken_languages['Dutch'] = true,
'Germany' => $spoken_languages['German'] = true,
'United Kingdom' => $spoken_languages['English'] = true,
};
}

var_export($spoken_languages);
// array ( 'Dutch' => true, 'French' => true, 'German' => true, 'English' => false, )

?>
up
2
tolga dot ulas at tolgaulas dot com
3 months ago
Yes it currently does not support code blocks but this hack works:

match ($foo){
'bar'=>(function(){
echo "bar";
})(),
default => (function(){
echo "baz";
})()
};
up
4
mark at manngo dot net
2 years ago
While you can’t polyfill a language construct, you can mimic the basic behaviour with a simple array.

Using example 2 above:

<?php
$food
= 'apple';
$return_value = match ($food) {
'apple' => 'This food is an apple',
'bar' => 'This food is a bar',
'cake' => 'This food is a cake',
};
print
$return_value;
?>

… you can get something similar with:

<?php
$food
= 'apple';
$return_value = [
'apple' => 'This food is an apple',
'bar' => 'This food is a bar',
'cake' => 'This food is a cake',
][
$food];
print
$return_value;
?>
up
-1
tm
2 years ago
If you are using a match expression for non-identity checks as described above make sure whatever you are using is actually returning `true` on success.

Quite often you rely on truthy vs. falsy when using if conditions and that will not work for match (for example `preg_match`). Casting to bool will solve this issue.
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