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    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"

    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 #3 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 #4 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 #5 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 8 notes

    up
    72
    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
    61
    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"),
        };
    }
    ?>
    up
    55
    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
    5
    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
    6
    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
    8
    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
    5
    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
    0
    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.
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