PHP's array_is_list() is underrated

Before PHP 8.1 I kept writing the same tiny helper: is this array a real list — keys 0, 1, 2 in order — or a map with names for keys? It comes up constantly, because JSON distinguishes a list from an object and PHP stores both in the same type.

The language ships it now:

array_is_list([1, 2, 3]);        // true
array_is_list([1 => 'a']);       // false
array_is_list(['a' => 1]);       // false
array_is_list([]);               // true — empty counts as a list

It only looks at keys, never at contents — and an empty array is a list. That’s usually what you want when you’re deciding whether to encode something as a JSON array or object, and it bites if “empty” is supposed to mean “nothing decided yet”. Same idea as not caching a silence: “no shape” and “the empty shape” are different answers.

One less utility to maintain.