[PHP-DEV] [Discussion] Revisiting typed closures

Hello internals,

I would like to revisit the idea of giving closures a typed call signature.

e.g. Closure(int, string): array -- enforced at the point a value crosses a
type boundary (an argument, a return, a property), the same places any other
type is checked.

Today a closure can only be typed as Closure or callable, neither of which
says anything about its parameters or return, even though that information is
right there.

I know this is not new ground: Callable Prototypes was declined in 2016, and
Garfield and Grekas shared two further RFCs in 2023 -- Structural Typing for
Closures, and Allow Closures to Declare Interfaces they Implement -- both still
in draft.

Before taking it further, I would like to know whether closure typing
is still considered worth pursuing -- or whether the topic is now regarded as
settled.

References:

- https://wiki.php.net/rfc/callable-types
- https://wiki.php.net/rfc/structural-typing-for-closures
- https://wiki.php.net/rfc/allow-closures-to-declare-interfaces-they-implement

Thanks.