Both of these functions are well-defined when used with a single
array argument -- rejecting this case was an artificial limitation.
This is not useful when called with explicit arguments, but removes
edge-cases when used with argument unpacking:
// OK even if $excludes is empty.
array_diff($array, ...$excludes);
// OK even if $arrays contains a single array only.
array_intersect(...$arrays);
This matches the behavior of functions like array_merge() and
array_push(), which also allow calls with no array or a single
array respectively.
Closes GH-6097.
This is targeting 8.0.
`$arg` seems like a poor choice of a name,
especially if the function were to have arguments added.
In many cases, the php.net documentation already has $array for these functions.
E.g. https://www.php.net/manual/en/function.array-intersect.php
I'd assume that since named arguments was added to 8.0 near the feature freeze,
PHP's maintainers had planned to make the names consistent
and gradually use the same name for docs and implementation.
