PHP: Hypertext Preprocessor

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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用户贡献的备注 9 notes

down

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);
}

down

Anonymous ¶

3 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"),

    };

}

?>

down

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.

down

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
};
?>

down

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";

down

tolga dot ulas at tolgaulas dot com ¶

8 months ago

Yes it currently does not support code blocks but this hack works:

match ($foo){
    'bar'=>(function(){
        echo "bar";
    })(),
    default => (function(){
        echo "baz";
    })()
};

down

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, )

?>

down

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;
?>

down

tm ¶

3 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.