PHP RFC: In Operator

• Version: 0.5
• Date: 2015-03-15
• Authors: Niklas Keller me@kelunik.com, Bob Weinand bobwei9@hotmail.com
• Status: Under Discussion
• First Published at: http://wiki.php.net/rfc/in_operator

This RFC adds a new in operator which simplifies contains checks for strings and arrays. Currently, we have to use in_array($needle, $haystack, true) or strpos($haystack, $needle) !== false. These functions have a inconsistent parameter order, so it's hard to remember which is the right one for each. The in operator makes these checks way more readable and lowers the cognitive load. Additionally, it also works for Traversable.

Add a new operator (expr1) in (expr2). It checks whether expr2 contains expr1.

It uses strict comparison (===) for array values / instances of Traversable and doesn't search recursively.

$contains = "foo" in ["a", "b", "c"]; // false
$contains = "foo" in ["foo", "bar"]; // true
$contains = "foo" in [["foo"], ["bar"]]; // false
$contains = "0e0" in ["0"]; // false, because of strict comparison
$contains = 0 in ["0"]; // false, because of strict comparison
 
$contains = ["foo"] in [["foo"], ["bar"]]; // true
$contains = ["foo"] in ["foo"]; // false

Traversables are only iterated until there's a match.

function gen () {
    yield "foo";
    yield "bar";
    // code below here wouldn't be executed if "bar" matches
    // because it stops if there's a match.
}
 
$contains = "bar" in gen(); // true
$contains = "baz" in gen(); // false

If $haystack is a string, it's a simple contains check.

$contains = "foo" in "foobar"; // true
$contains = "php" in "foobar"; // false

Other expressions than mixed in array|Traversable or string in string throw an EngineException.

It's strict because otherwise something like “foo” in [0] would pass.

It should have the same precedence as instanceof, so it's possible to negate it:

if (!$input in $validValues) {
    // ...
}

New reserved keyword in. This affects function, constant, class and method names.

Next major release, at the time of writing PHP 7.

A T_IN constant for use with ext/tokenizer has been added.

There could be a syntax that allows to check for multiple values at once, e.g.

$contains = ...["foo", "bar"] in ["foo", "baz", "bar"];

Requires a 2/3 majority. Even if it passes, it will only get merged if the context sensitive lexer gets merged.

• https://github.com/php/php-src/pull/1121

Keep this updated with features that were discussed on the mail lists.

• v0.5: Removed integer support, so the strictness is consistent.
• v0.4: Removed possibility to check multiple values using an array.