array_key_casting.md

Array key casting

General idea

When using arrays, PHP automatically casts numeric-string keys to int if the string is exactly the same as an integer. For example:

<?php

$values = [
    '01' => '01',
    '10' => '10',
    '10 ' => '10 ',
];

foreach ($values as $key => $value) {
    echo "key type is: " . gettype($key) . ", key value is [$key] \n";
}

The output of that code is:

key type is: string, key value is [01]
key type is: integer, key value is [10]
key type is: string, key value is [10 ]

i.e. the key '10' has been converted from a string to an int.

This has some implications:

• array_flip(array_flip($a)) !== $a

• array_search('10', $a) is an int when array_search('01', $a) is still a string. Someone using strict types and passing the result to a function expecting a string could end with an unexpected crash.

• general astonishment that this occurs, which leads to people thinking PHP is crap.

Hurdles to overcome

BC compatibility

Changing this behaviour would a large and very subtle BC break. If it was to be 'just changed' there would need to be a version that gives a deprecation warning when it occurs.

Alternatively some other mechanism to allow people to opt into a different behaviour for arrays would need to occur.

Internal engine has a default mode

One of the suggestions to fix this, is to introduce declare(strict_arrays = 1);.

That might have similar problems to how the engine is in weak mode by default, where the behaviour of code in callbacks changes depending on whether the code was called by the engine internally, or from a PHP file that has declare(strict_arrays = 1);.

Forecast

This is certainly a problem that should be solved at some point.

My suspicion is that refactoring arrays completely in a larger piece of work might be more productive. Rather than just poking a single part of arrays, figuring out what to do about ArrayAccess at the same time, might produce a

Notes