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Date: Mon, 23 May 2016 22:19:18 +0300
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References: <op.yhw6ft0mc9evq2@nikita-work-box> <CAFMT4NrXPDrjOTda_0nL-1AL7MvkK=DC32XTQwktsrAMGM687A@mail.gmail.com>
To: Levi Morrison <levim@php.net>
Subject: Re: [PHP-DEV] [RFC] [Vote] Callable types (now: Callable prototypes)
From: inefedor@gmail.com (Nikita Nefedov)


> On 23 May 2016, at 19:31, Levi Morrison <levim@php.net> wrote:
>=20
>> On Mon, May 23, 2016 at 8:27 AM, Nikita Nefedov <inefedor@gmail.com> wrot=
e:
>> Evening internals,
>>=20
>> With this message I'd like to go to vote
>> with the Callable prototypes RFC targeted at 7.1:
>> https://wiki.php.net/rfc/callable-types
>>=20
>> We've renamed it (previously was "Callable types") as RFC names often
>> dictate how users will call the feature and I want it to be more
>> accurate/descriptive.
>>=20
>> Also the reflection part was added although I'm short on time currently,
>> so implementation for that will be ready later. (speaking of implementati=
on,
>> it also currently doesn't use cache_slots - also something I'll add when
>> I have a little bit of time)
>>=20
>> --
>> PHP Internals - PHP Runtime Development Mailing List
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>=20
> A quick question before I vote: do callable prototypes allow for
> default parameters in the signature? There are examples for having a
> function passed that has a default parameters but I am not seeing it
> anywhere in the callable prototype definition so I thought I'd ask.

Hey Levi,

Although it could be done as a later RFC, my stance on it is that default va=
lues don't belong to the prototype of the function.

Why I think that callable typehint doesn't need default values for params is=
: you either need this parameter to exist and even if there are cases where y=
ou'd like to pass some kind of 'default' value implicitly, you as a caller s=
houldn't impose on the callee responsibility to have this same value in his d=
efinition and instead just pass your argument explicitly... or if you don't n=
eed this parameter (as in you don't plan to pass anything explicitly) then y=
ou should just ask for a function without this parameter as there is clearly=
 no need for it at all.

Moreover I would argue interfaces have it wrong here too: the fact that defa=
ult values are part of an interface yet their invariance is not enforced, yi=
elds an interesting sort of possible LSP violation. F.e. if we have an inter=
face Logger (a completely unreal example but it shows what can go wrong) wit=
h function 'log($message, $level =3D LOG_DEBUG);' and a funny implementation=
 that decided to change default value of $level to LOG_ALERT, then all calle=
rs of Logger#log who relied on the fact that level if not specified, will be=
 LOG_DEBUG, who also happen to get the funny implementation of Logger will p=
roduce unneeded noise in the logs with their alert level messages which were=
 intended to be debug messages :(=