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Date: Fri, 06 Feb 2026 14:30:11 -0600
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Subject: Re: [PHP-DEV] [RFC] Partial Function Application for instance of non-static
 methods ("$this")
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From: larry@garfieldtech.com ("Larry Garfield")

On Fri, Feb 6, 2026, at 10:43 AM, Tim D=C3=BCsterhus wrote:
> Hi
>
> On 1/22/26 17:41, Larry Garfield wrote:
>> More spitballing on my previous reply:
>>=20
>> class Test {
>>    public function stuff(int $a) {}
>> }
>>=20
>> (Test)?->stuff(?);
>
> As mentioned in the sibling mail, this is existing syntax and thus=20
> doesn't work.

Sure, but we can fiddle with the details to find something that works.  =
I also suggested something like these to Arnaud off-list:

(?: Test)->stuff(?);
(Test ?)->stuff(?);
((Test)?)->stuff(?);


> Keeping full type information is the main benefit of PFA over =E2=80=9C=
just=20
> write a Closure=E2=80=9D. Being able to reorder parameters as part of =
partial=20
> application is another explicit feature that would not be supported by=20
> that syntax.

Honestly, I don't much care about the reordering.  And with this approac=
h you'd still be able to reorder the method params, just keep the object=
 as first arg.

>> That would then be a lot easier to write in cases where you're just d=
ropping a $this->stuff() call into a pipe chain but want to receive $thi=
s.
>
> The use case for partially applying `$this` is in cases where you need=
 a=20
> =E2=80=9Cfunction handle=E2=80=9D, that's why the examples are ones wh=
ere the resulting=20
> Closure is passed as a parameter to another function.
>
> Within a pipe chain you would just use the regular `->` operator on th=
e=20
> result of the previous step:
>
>      $result =3D (trim($username)
>          |> $repository->findBy(name: ?)
>          )->getId();
>
> It would also naturally support `?->` in case your repository returns=20
> `null` when the user cannot be found.

Directly in a pipe chain, sure.  However, I would see this as most usefu=
l as a callback to array_map et al (or future equivalents).

Eg:

import_stuff()
  |> array_filter(?, (?)->hasField('comment')
  |> array_map((?)->save(), $records)
;

In this case, the only thing being partialed is the object on which to i=
nvoke.  So there's no need to think about reordering the params in the f=
irst place: There's just one.

Needing to specify the type in this case:

import_stuff()
  |> array_filter(?, Record::hasField('comment', ...)
  |> array_map(Record::save(...), $records)
;

Just adds more noise, and IMO creates confusion between static and non-s=
tatic methods.

--Larry Garfield