PHP RFC: In Operator

• Version: 0.3
• Date: 2015-02-20
• Authors: Niklas Keller me@kelunik.com, Bob Weinand bobwei9@hotmail.com
• Status: Draft
• 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. 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

function gen () {
    yield "foo";
    yield "bar";
}
 
$contains = "bar" in gen();

If the first parameter is an array , it checks for every element whether it's contained in the $haystack or not. This is an advantage compared to in_array. It doesn't check the values in $needle recursively, so it's still possible to check if an array contains another array, but makes checking multiple scalars easier:

$contains = ["foo", "bar"] in ["foo", "baz", "bar"]; // true
$contains = ["foo", "bar", "baz"] in ["foo", "bar"]; // false
$contains = [["foo", "bar"]] in [["foo", "bar"], ["foo", "baz"]]; // true
$contains = [["foo", "bar"]] in ["foo", "bar"]; // false

For strings, it behaves exactly like strpos($haystack, $needle) !== false:

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

Objects are not supported, because we already have isset here.

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

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, constants, 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.

Make sure there are no open issues when the vote starts!

None.

Requires a 2/3 majority, simple yes / no vote.

TBD

TBD

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