phpstanPlayground.arrayDimFetchCast

Code example

<?php declare(strict_types = 1);

$a = ['foo' => 1, 'bar' => 2];

echo $a['1'];  // key '1' (string) will be cast to 1 (int)
echo $a[null]; // key null will be cast to '' (string)
echo $a[2.5];  // key 2.5 (float) will be cast to 2 (int)
echo $a[true]; // key true (bool) will be cast to 1 (int)

Why is it reported?

PHP silently casts array keys to int or string when accessing array elements. A numeric string like '1' is cast to the integer 1, null becomes the empty string '', floats are truncated to integers, and booleans become 0 or 1. This means the accessed key may not match what the developer intended, leading to unexpected values or missing entries.

This rule is only active on the PHPStan playground.

Learn more: Why Array String Keys Are Not Type-Safe in PHP

How to fix it

Use array keys that match the expected type without implicit casting:

 $a = [1 => 'one', 2 => 'two'];

-echo $a['1'];
+echo $a[1];

For null keys, use the explicit string equivalent:

-echo $a[null];
+echo $a[''];

For float keys, use the truncated integer directly:

-echo $a[2.5];
+echo $a[2];

For boolean keys, use the corresponding integer:

-echo $a[true];
+echo $a[1];