Re: [PHP-DEV] [Discussion] Revisiting typed closures

> I would rather wait for generics and possibly make Closure a generic type.
>
> — Rob

Hi Rob,

I don't think generics help here. PHP doesn't have generics at all
yet, and realistically they're at least a couple of years away. But
even once they land, they wouldn't solve this.

Making `Closure` generic (e.g., say `Closure<Input, Output>` ) would
require `Input` to be variadic to stand in for a closure's parameter
list, and variadic generics are a different beast entirely.

They've never appeared in any proposal, they don't really make sense
for a number of reasons, and if they were ever added at all, it would
be years after generics themselves. So "wait for generics" here
effectively means waiting indefinitely. And arity aside, a generic
`Closure<...>` still couldn't express which arguments are required
versus optional, nor type a closure that is itself generic. A
dedicated syntax like `fn<T>(T, string=): T` handles all of it
cleanly:

- The generic parameter ( `<T>` )
- Te required and optional arguments ( `=` marker )
- The return type ( following `:` )

Cheers,
Seifeddine