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Date: Fri, 21 Mar 2025 14:32:58 +0000
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Subject: Re: [PHP-DEV] [RFC] [Discussion] Never parameters
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From: imsop.php@rwec.co.uk ("Rowan Tommins [IMSoP]")

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On 21/03/2025 11:50, Tim Düsterhus wrote:
> Am 2025-03-20 21:27, schrieb Matt Fonda:
>> If an interface adds a method but makes no promises about what 
>> parameters
>> it accepts, then why is it part of the interface in the first place--why
>> add a method that can't be used?
>
> It would more cleanly allow for userland / PHPDoc-based generics, 
> while still providing some engine-enforced type safety. Consider this 
> example (not sure if I got the syntax completely right):
>
>     /** @template T */
>     interface Comparable {
>         /** @param T $other */
>         public function compareTo(never $other): int;
>     }
>
>     /** @implements Comparable<Number> */
>     final class Number implements Comparable {
>         public function compareTo(Number $other): int { return $this 
> <=> $other; }
>     } 


I think I agree with Matt on this: the interface isn't making any usable 
promises about that method.

In this example, Comparable is a kind of "abstract interface" - in order 
to actually make use of it, you need to specialise it.

Declaring that a class implements a template interface is like 
inheriting an abstract method: either you fill in the type parameter 
("class Foo implements Comparable<Foo> { ... }"), or the class is also a 
template ("class Foo<A> implements Comparable<A> { ... }")


I don't think the language should pretend to support something that it 
doesn't - if the contract is actually enforced by a third-party tool 
reading docblocks, put the contract in a docblock:

     /**
        * @template T
        * @method compareTo(T $other): int;
        */
     interface Comparable {
     }

     /** @implements Comparable<Number> */
     final class Number implements Comparable {
         public function compareTo(Number $other): int { return $this 
<=> $other; }
     }


-- 
Rowan Tommins
[IMSoP]

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    <div class="moz-cite-prefix">On 21/03/2025 11:50, Tim Düsterhus
      wrote:<br>
    </div>
    <blockquote type="cite"
      cite="mid:ab983707b9845d5288305017205f27a1@bastelstu.be">Am
      2025-03-20 21:27, schrieb Matt Fonda:
      <br>
      <blockquote type="cite" style="color: #007cff;">If an interface
        adds a method but makes no promises about what parameters
        <br>
        it accepts, then why is it part of the interface in the first
        place--why
        <br>
        add a method that can't be used?
        <br>
      </blockquote>
      <br>
      It would more cleanly allow for userland / PHPDoc-based generics,
      while still providing some engine-enforced type safety. Consider
      this example (not sure if I got the syntax completely right):
      <br>
      <br>
          /** @template T */
      <br>
          interface Comparable {
      <br>
              /** @param T $other */
      <br>
              public function compareTo(never $other): int;
      <br>
          }
      <br>
      <br>
          /** @implements Comparable&lt;Number&gt; */
      <br>
          final class Number implements Comparable {
      <br>
              public function compareTo(Number $other): int { return
      $this &lt;=&gt; $other; }
      <br>
          }
    </blockquote>
    <p><br>
    </p>
    <p>I think I agree with Matt on this: the interface isn't making any
      usable promises about that method.<br>
    </p>
    <p>In this example, Comparable is a kind of "abstract interface" -
      in order to actually make use of it, you need to specialise it. </p>
    <p>Declaring that a class implements a template interface is like
      inheriting an abstract method: either you fill in the type
      parameter ("class Foo implements Comparable&lt;Foo&gt; { ... }"),
      or the class is also a template ("class Foo&lt;A&gt; implements
      Comparable&lt;A&gt; { ... }")</p>
    <p><br>
    </p>
    <p>I don't think the language should pretend to support something
      that it
      doesn't - if the contract is actually enforced by a third-party
      tool reading docblocks, put the contract in a docblock:</p>
    <p>    /** <br>
             * @template T<br>
             * @method compareTo(T $other): int;
      <br>
             */
      <br>
          interface Comparable {<br>
          } <br>
    </p>
    <p>    /** @implements Comparable&lt;Number&gt; */
      <br>
          final class Number implements Comparable {
      <br>
              public function compareTo(Number $other): int { return
      $this &lt;=&gt; $other; }
      <br>
          }
    </p>
    <p><br>
    </p>
    <pre class="moz-signature" cols="72">-- 
Rowan Tommins
[IMSoP]</pre>
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