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Date: Wed, 22 Apr 2020 17:33:29 +0000
To: Rowan Tommins <rowan.collins@gmail.com>
Cc: "internals@lists.php.net" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Typed callable properties
From: moliata@protonmail.com (moliata)

Hello,

thank you for the comment! Yes, indeed I was raising a discussion on whethe=
r we
should allow making typed callable properties for improved language's
consistency (given that parameter/return type hints can be set to callable)=
. As
one of the solutions, I mentioned that we could just ignore the
scope/context-dependent problems for the time being.

In regards to your comment on `Closure::fromCallable()`, I do also agree th=
at
it is quite verbose and a potential performance hit and as such, this isn't=
 the
way to go. As an example, let's imagine a framework that allows registering
routes to callables. If we wanted to completely type-hint the entire framew=
ork,
we would have to make typed Closure properties and in the `addRoute()` func=
tion
used `Closure::fromCallable()` to convert every single callable into a clos=
ure
object. So, huge applications with thousands of routes would be potentially
affected by this additional overhead.

Best regards,
Benas Seliuginas
=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90 Original Me=
ssage =E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90
On Wednesday, April 22, 2020 7:30 PM, Rowan Tommins <rowan.collins@gmail.co=
m> wrote:

> On 22/04/2020 16:01, Micha=C5=82 Brzuchalski wrote:
>
> > I agree, a callable brings as much information as a resource type - you
> > know the type
> > but are unable to use it without additional information.
>
> While this is true, it's somewhat orthogonal to the question Benas
> raised in this thread - namely, how to handle values that are callable
> in one scope but not another.
>
> That is, is the following code valid (error-free) or not?
>
> delegate Reducer (?int $sum, int $item =3D 0): int;
> class X {
> =C2=A0=C2=A0=C2=A0 private static function myPrivateMethod(?int $sum, int=
 $item =3D 0):
> int {
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return 0;
> =C2=A0=C2=A0=C2=A0 }
> =C2=A0=C2=A0=C2=A0 public static function runReducer(Reducer $r) {
> =C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0=C2=A0 return $r(0, 0);
> =C2=A0=C2=A0=C2=A0 }
> }
> echo X::bar(['X', 'myPrivateMethod']);
>
> The equivalent code with a type constraint of "callable" currently runs
> fine, even though passing the same value to a different function would
> fail due to scoping. Making the delegate-constrained version throw an
> error for any private or protected method would just trade one
> inconsistency for another.
>
> A more reasonable restriction, IMO, would be to say that delegates only
> match Closure instances (and possibly other objects with a public
> __invoke method), not the various string and array syntaxes that
> "callable" currently allows. The case above would then need to bind the
> private method into a closure that is callable everywhere, e.g. using
> Closure::fromCallable([self::class, 'myPrivateMethod']);
>
> The obvious downside is that Closure::fromCallable is both verbose and a
> potential performance hit. So it seems we're back again to wanting a new
> syntax to succinctly and optimally generate such a closure. For
> instance, in the discussion of ::func, one suggestion was
> "$closure=3D{self::myPrivateMethod};" and more recently it was mentioned
> that a variant of partial application is to not actually bind anything,
> and write "$closure=3Dself::myPrivateMethod(?, ?);"
>
> Regards,
>
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>
> Rowan Tommins (n=C3=A9 Collins)
> [IMSoP]
>
> -----------------------------------
>
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