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Date: Wed, 19 Jan 2022 10:07:20 -0500
Message-ID: <CAPKYkKyDUyHymMQU8YG_mfn41J8ZEhx1CFuqSJt90M-CaPt-fw@mail.gmail.com>
To: Jordan LeDoux <jordan.ledoux@gmail.com>
Cc: Rowan Tommins <rowan.collins@gmail.com>, PHP internals <internals@lists.php.net>
Content-Type: multipart/alternative; boundary="000000000000be441405d5f0be03"
Subject: Re: [PHP-DEV] RFC: Trait expects interface
From: chasepeeler@gmail.com (Chase Peeler)

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On Tue, Jan 18, 2022 at 3:55 PM Jordan LeDoux <jordan.ledoux@gmail.com>
wrote:

> On Tue, Jan 18, 2022 at 11:13 AM Rowan Tommins <rowan.collins@gmail.com>
> wrote:
>
> >
> > The difference with the "trait requires interface" proposal is that I
> > don't understand what advantage it gives the author of the trait. What
> > decisions can you make as a library developer because you've said "users
> > of this trait must implement the matching interface" as opposed to "...
> > can implement the matching interface"?
> >
> > It's possible there is some advantage I'm missing, but so far nobody
> > seems to have presented it.
> >
> >
> Well, the trait doesn't necessarily have to fulfill the entire interface,
> first of all. As you mentioned, this can be worked around using abstracts
> in the trait. However, what if you're dealing with return values within the
> trait?
>
> Suppose I have something like this:
>
> trait ArithmeticTrait {
>     public function add(float $val): NumberInterface {
>         // Do math
>
>         return $this;
>     }
>
>     public function addmul(float $val): NumberInterface {
>         $added = $this->add($val);
>
>         if ($added->isPositive()) {
>             // Do stuff
>         }
>
>         return $this;
>     }
> }
>

This can still be handled with abstract methods


trait ArithmeticTrait {
    public function add(float $val): NumberInterface {
       $n = $this->getNumberInterface();
        // Do math

        return $n;
    }

    public function addmul(float $val): NumberInterface {
        $n = $this->getNumberInterface();
        $added = $this->add($val);

        if ($added->isPositive()) {
            // Do stuff
        }

        return $n;
    }

   abstract protected function getNumberInterface(): NumberInterface;
}

class Foo {
  use  ArithmeticTrait;

  protected NumberInterface $n;

  protected function getNumberInterface() : NumberInterface {
     return $this->n;
  }
}


>
> In this situation, the return value of the trait requires that $this
> implements the NumberInterface, however there is no way for the trait
> itself to enforce this.
>
> Jordan
>


-- 
Chase Peeler
chasepeeler@gmail.com

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