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Date: Fri, 25 Jan 2019 12:05:21 +0100
Message-ID: <CAF+90c8-txCpDYhJLNEMTNQtHtxgx=Ty0ydadRtS_gE-uWcOxA@mail.gmail.com>
To: Andrey O Gromov <AGromov@alfabank.ru>
Cc: PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="00000000000087f0720580464e79"
Subject: Re: [PHP-DEV] Proposal fo "Code-free constructors declaration"
From: nikita.ppv@gmail.com (Nikita Popov)

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On Fri, Jan 25, 2019 at 11:44 AM Nikita Popov <nikita.ppv@gmail.com> wrote:

> On Wed, Jan 23, 2019 at 1:33 PM Andrey O Gromov <AGromov@alfabank.ru>
> wrote:
>
>> Full description
>> https://wiki.php.net/rfc/code_free_constructor
>> Draft realisation
>> https://github.com/php/php-src/compare/master...rjhdby:constructor
>>
>> "Code free" constructor is constructor with only purpose to directly set
>> object properties from received parameters and, optionally, call parent
>> constructor.
>>
>> Main idea is to move such constructor declaration inside class
>> declaration.
>>
>> Simple example:
>>
>> Current syntax
>> class A extends B{
>>     public $prop;
>>
>>     public function __construct($prop){
>>         parent::__construct("BlaBla", $prop);
>>         $this->prop = $prop;
>>     }
>> }
>>
>> Proposed syntax
>> class A($prop) extends B("BlaBla", $prop) {
>> }
>>
>> With respect, Andrey.
>
>
> Two alternatives you might want to consider:
>
> * https://wiki.php.net/rfc/automatic_property_initialization => Proposed
> function public function __construct(int $this->x, int $this->y) {}, which
> avoids the need for explicit property assignments in the ctor. However, the
> property still needs to be declared separately.
>
> *
> https://docs.hhvm.com/hack/other-features/constructor-parameter-promotion
> => Uses public function __construct(public int $x, public int $y) {} to
> declare properties in-line in the constructor.
>
> I think that *if* we want to add some kind of sugar of this type, then I'd
> strongly prefer the syntax used by Hack than the one proposed here. It
> makes a lot more sense to me intuitively, probably because the property
> declarations still looks like normal property declarations, they just occur
> in-line in the ctor.
>
> Nikita
>

To add to this: While I can totally understand the motivation to avoid the
property/constructor boilerplate (where the property name needs to be
repeated four times), I think that this is really solving the wrong
problem. The problem is the need to have a constructor at all.

Both this RFC and the two alternatives mentioned above really target the
case of "dumb" constructors that don't really do anything beyond assigning
properties from ctor arguments. I think that that is better solved by
adding a first-class syntax for object construction. I have something
roughly like this in mind:

class Point {
    public int $x;
    public int $y;
    public int $z;
}

// (syntax just a dummy)
$origin = new Point { x = 0, y = 0, z = 0 };

Where the object initialization syntax ensures that all properties that
don't have defaults are initialized. Especially now that we have typed
properties and it is feasible to have data objects with just public typed
properties, I think that this is the way to avoid ctor boilerplate, rather
than making it simpler to write that boilerplate.

Nikita

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