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Date: Thu, 8 Apr 2021 15:55:25 +0500
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To: Saif Eddin Gmati <azjezz@protonmail.com>
Cc: "internals@lists.php.net" <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Empower Callables with Function Signature Hints
From: office.hamzaahmad@gmail.com (Hamza Ahmad)

Hello,
I thanks Saif for adding to my argument and providing with the list of
other languages/tools that support such a functionality.
As Saif has mentioned about "typesafe callables" RFC that is now
inactive, I want to also point out toward another rfc that was
declined.
It was Callable Prototype RFC that had sought for the similar
functionality. https://wiki.php.net/rfc/callable-types
Python also provides with a library ever since 3.5:
https://docs.python.org/3/library/typing.html
After looking at the prior RFCs, I feel like that it requires a fresh
discussion. Because there are several syntax to choose from, a
separate vote will only be held for this.
Best
Hamza Ahmad

On 4/7/21, Saif Eddin Gmati <azjezz@protonmail.com> wrote:
> Hello Hamza,
>
> I think this is something that has been discussed here before.
>
> function types already exist in HackLang:
> https://docs.hhvm.com/hack/functions/introduction#function-types,
>
> And, if we would follow the same syntax `(function(T, T): T)` or
> `(callable(T, T): T)`, PHP needs to first support parentheses in
> type declaration ( grouping ), which currently it doesn't ( i.e: `functio=
n
> baz((string|bar) $foo): void {}` becomes valid ).
>
> And just to note, function types are also supported by static analysis to=
ols
> such as Psalm (
> https://psalm.dev/docs/annotating_code/type_syntax/callable_types/ ) and
> PHPStan ( https://phpstan.org/writing-php-code/phpdoc-types#callables ), =
so
> i suppose if PHP is to support typed callables, it should take inspiratio=
n
> from these tools.
>
> There's also an alternative syntax that was proposed back in 2016 for PHP
> 7.1, but it seems like the RFC was abandoned:
> https://wiki.php.net/rfc/typesafe-callable
>
> Cheers,
>
> Saif.
>
> =E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90 Original =
Message =E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90=E2=80=90
> On Wednesday, April 7, 2021 11:58 AM, Hamza Ahmad
> <office.hamzaahmad@gmail.com> wrote:
>
>> Hello Internals,
>> I want to request making possible to catch functions with wrong signatur=
e
>> when passed as callable. In other words, when a function or a method is
>> passed as callable value, PHP will first confirm whether the function is
>> of
>> the write callable type that the function being executed requires. It
>> will
>> help catch silent errors.
>> Currently, PHP does following:
>>
>
>> 1.  Confirms whether a callable is valid.
>> 2.  Passes the callable value to a function, and the execution starts.
>> 3.  If the passed function receives values which's type is different tha=
n
>>     function signature, PHP throws an error.
>>
>
>> 4.  If passed function returns nothing, the variable that wanted a value
>> from
>>     the passed function receives null.
>>
>
>> 5.  As a result, the unexpected results emerge.
>>     To resolve this issue, I propose to introduce a mechanism that allow=
s
>> to
>>     hint callable signatures. To understand the spirit of this request,
>> look at
>>     the similar functionality that Angel Script Project provides with.
>>
>
>> 6.  One defines a function definition.
>> 7.  Use its name to hint the same signature.
>> 8.  The compiler alerts about the incorrect signature before passing thi=
s
>> to
>>     a function.
>>     If I could do this in PHP, I would write like following:
>>     `funcdef preg_replace_callback_hint(array $matches) : string;`
>>     If I accidently pass a callable which's signature is different than
>> desired
>>     function call, the error is caught earlier.
>>     This message does not suggests syntax; it only points to a problem
>> and
>>     suggests a solution. Any volunteers that would love to come up with
>> syntax
>>     and implement this?
>>     I am curious to see the feedback.
>>     Regards
>>     Hamza Ahmad
>>
>
>>     --
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>>
>
>