Re: [Discussion] Revisiting typed closures

On Wed, 1 Jul 2026 at 15:43, Matheus Martins <mathrm@gmail.com> wrote: > > 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. Hi Matheus, I'm in favor of adding this. However, syntax wise, i would rather we re-use the fn keyword, e.g: - fn(int): string - fn(string, int=): string (= indicates the parameter is optional) - fn(...string): string (... indicates the parameter is variadic) - fn(&string): void (& indicates the parameter is by-reference) I also think restricting this to allow only Closure instance inputs is the right approach ( given that we have FCC ), as i think type checking array callables, and strings would be annoying and probably wasteful. Cheers, Seifeddine.