New in PHP 8: the match Expression中文EN

PHP 8 alpha2 is out, and it recently introduced a new keyword: match. Its role is somewhat similar to switch.

I'm usually indifferent to syntactic sugar, but I find this one rather interesting — and "match" is a nice-looking word. So what does it do?

In the past we often used switch for value-conversion work, like:

switch ($input) {
    case "true":
        $result = 1;
    break;
    case "false":
        $result = 0;
    break;
    case "null":
        $result = NULL;
    break;
}

(Yes, some of you will say: who writes it like that, why not just use an array for the conversion? Come on, this is an example — arrays only give you string and integer keys; what if the key needs to be some other expression, or you want multiple keys mapping to one value, right?)

Now with the match keyword, it becomes something like:

$result = match($input) {
        "true" => 1,
        "false" => 0,
        "null" => NULL,
};

Unlike switch, match directly returns a value, so you can assign it straight to $result.

And just as switch lets several cases share one block, match lets several conditions share one arm, for example:

$result = match($input) {
    "true", "on" => 1,
    "false", "off" => 0,
    "null", "empty", "NaN" => NULL,
};

One important difference from switch: with switch we often ran into this eerie problem:

$input = "2 person";
switch ($input) {
    case 2:
        echo "bad";
    break;
}

You'd find "bad" actually gets printed, because switch uses loose comparison (==). match doesn't have this problem — it uses strict comparison (===), requiring both value and type to be exactly equal.

Also, when the input satisfies none of the conditions in a match, it throws an UnhandledMatchError exception:

$input = "false";
$result = match($input) {
        "true" => 1,
};

You get:

Fatal error: Uncaught UnhandledMatchError: Unhandled match value of type string

So you never have to worry that an incomplete set of match conditions will cause unpredictable errors.

One more thing to note: match is a keyword, which means from PHP 8 onward it cannot appear in namespace or class names. If your project has a class named match:

class Match {}

you'll get a syntax error starting with PHP 8. Method names, of course, may still use it.

For details, see the RFC: Match Expression

That's all.