[RFC] Add is_list(mixed $value): bool to check for list-like arrays

Hi Ben,

I don’t think changing the name changes my concern, but as Tyson
pointed out:

These idiosyncrasies of php and unintuitive behaviors existed prior
to this RFC.

I’m generally +1 on this RFC, but as I think about it, maybe there is a
problem with the name. If we choose to introduce a pure list construct
at some point, then is_list() may cause confusion (or maybe it won’t,
if it can be made to return true for a zero-indexed, standard PHP
array and a list, whatever that might look like in the language).

For the possibility of list being added to the language:
The syntax conflict with list($a) = ... may cause issues with supporting it in the parser,
and confuse people learning the language,
but I can still see it as possible since the parser conflict also means that it wouldn't conflict with existing names (if that were fixed).
The fact that my RFC is also using "list" to refer to sequential arrays starting with 0 may encourage that name over vec
in the future, in combination with SplDoublyLinkedList already existing.

• I guess list[$a, $b] may be usable as shorthand for list creation but that's out of the scope of this rfc

So the naming's definitely a potential concern. My earlier idea of is_array_list() or is_array_a_list() may help avoid that ambiguity if that's a concern.
I'd still prefer short terms for common language concepts - zero_indexed isn't a commonly used phrase

Cheers,
Tyson