offsetAccess.invalidOffset

Code example

<?php declare(strict_types = 1);

$a = [];

$foo = $a[new DateTimeImmutable()];
$a[[]] = $foo;

Why is it reported?

The value used as an array key is not a valid array key type. PHP arrays only accept int and string as keys. Using objects, arrays, or other types as array keys results in a runtime error.

Types that are implicitly converted to int or string (like bool, float, or null) may also be reported depending on the PHP version and PHPStan configuration, because these implicit conversions are often unintentional and can lead to subtle bugs.

How to fix it

Convert the value to a valid array key type:

-$foo = $a[new DateTimeImmutable()];
+$foo = $a[$dateTime->format('Y-m-d')];

-$a[[]] = $foo;
+$a[implode(',', $keys)] = $foo;

If you need to use objects as keys, use SplObjectStorage or WeakMap:

-$a = [];
-$a[new DateTimeImmutable()] = 'value';
+$a = new SplObjectStorage();
+$a[new DateTimeImmutable()] = 'value';