Newsgroups: php.internals
Path: news.php.net
Xref: news.php.net php.internals:125259
Content-Type: multipart/alternative;
 boundary="------------LUUITnlHEQ15yUtwlHNJKF2r"
Message-ID: <a5e8faf3-e3d7-41c0-98b2-0999ee7444bb@scriptfusion.com>
Date: Mon, 26 Aug 2024 10:26:55 +0100
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PHP-DEV] [RFC] Default expression
To: internals@lists.php.net
References: <0c8ed5d6-5507-4c41-8d7f-05d14ba8aa4c@scriptfusion.com>
 <15301ee5-7964-4f0b-8804-a19f95f43152@gmx.net>
Content-Language: en-GB
In-Reply-To: <15301ee5-7964-4f0b-8804-a19f95f43152@gmx.net>
From: bilge@scriptfusion.com (Bilge)

This is a multi-part message in MIME format.
--------------LUUITnlHEQ15yUtwlHNJKF2r
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 8bit

On 26/08/2024 10:03, Andreas Leathley wrote:
> On 24.08.24 18:49, Bilge wrote:
>
> For me there is another question. When using interfaces and classes,
> default values can be introduced, like this:
>
> interface CompressionInterface
> {
>     public function compress(string $data, int $level): string;
> }
>
> class GzipCompression implements CompressionInterface
> {
>     public function compress(string $data, int $level = 4): string
>     {
>         // do something
>     }
> }
>
> When I have the GzipCompression class, I would know there is a default
> value for $level, but when using the interface there might or might not
> be a default value, depending on the implementation. As far as I read
> the RFC, using "default" when there is no default would lead to a
> runtime exception, but there is no way of finding out if there is a
> default if you do not already know. Being able to test that could be
> useful, although I am not sure about the syntax for that. In the example
> when getting CompressionInterface, I might test for the existence of a
> default value of $level and leave it at the default if there is a
> default (maybe I know that some implementations have a default value,
> others don't). One could test the specific implementation with
> instanceof checks, but the advantage of "default" could be that you do
> not need to know the implementation and could only adapt to possibly
> defined default values.

Hi Andreas,

Thanks for this question; I find this super interesting because it's 
something we haven't thought about yet. I must admit I completely 
overlooked that, whilst an interface /can/ require implementers to 
specify a default, in the case that they do not, it is still valid for 
implementations to selectively elect to provide one. Therefore I can 
append to your example the following case (I removed the `string` return 
type for now):

class ZipCompression implements CompressionInterface
{
     public function compress(string $data, int $level)
     {
         var_dump($level);
     }
}

new GzipCompression()->compress('', default ?? 6);
new ZipCompression()->compress('', default ?? 6);

In this case, we get the following output:

int(4)
Fatal error: Uncaught ValueError: Cannot pass default to required 
parameter 2 of ZipCompression::compress()

I would like to fix this if possible, because I think this should be 
valid, with emphasis on /if possible/, because it may be prohibitively 
complex. Will update later.

Cheers,
Bilge

--------------LUUITnlHEQ15yUtwlHNJKF2r
Content-Type: text/html; charset=UTF-8
Content-Transfer-Encoding: 8bit

<!DOCTYPE html>
<html>
  <head>
    <meta http-equiv="Content-Type" content="text/html; charset=UTF-8">
  </head>
  <body>
    <div class="moz-cite-prefix">On 26/08/2024 10:03, Andreas Leathley
      wrote:<br>
    </div>
    <blockquote type="cite"
      cite="mid:15301ee5-7964-4f0b-8804-a19f95f43152@gmx.net">On
      24.08.24 18:49, Bilge wrote:
      <br>
      <br>
      For me there is another question. When using interfaces and
      classes,
      <br>
      default values can be introduced, like this:
      <br>
      <br>
      interface CompressionInterface
      <br>
      {
      <br>
          public function compress(string $data, int $level): string;
      <br>
      }
      <br>
      <br>
      class GzipCompression implements CompressionInterface
      <br>
      {
      <br>
          public function compress(string $data, int $level = 4): string
      <br>
          {
      <br>
              // do something
      <br>
          }
      <br>
      }
      <br>
      <br>
      When I have the GzipCompression class, I would know there is a
      default
      <br>
      value for $level, but when using the interface there might or
      might not
      <br>
      be a default value, depending on the implementation. As far as I
      read
      <br>
      the RFC, using "default" when there is no default would lead to a
      <br>
      runtime exception, but there is no way of finding out if there is
      a
      <br>
      default if you do not already know. Being able to test that could
      be
      <br>
      useful, although I am not sure about the syntax for that. In the
      example
      <br>
      when getting CompressionInterface, I might test for the existence
      of a
      <br>
      default value of $level and leave it at the default if there is a
      <br>
      default (maybe I know that some implementations have a default
      value,
      <br>
      others don't). One could test the specific implementation with
      <br>
      instanceof checks, but the advantage of "default" could be that
      you do
      <br>
      not need to know the implementation and could only adapt to
      possibly
      <br>
      defined default values.
      <br>
    </blockquote>
    <p>Hi Andreas,</p>
    <p>Thanks for this question; I find this super interesting because
      it's something we haven't thought about yet. I must admit I
      completely overlooked that, whilst an interface <i>can</i>
      require implementers to specify a default, in the case that they
      do not, it is still valid for implementations to selectively elect
      to provide one. Therefore I can append to your example the
      following case (I removed the `string` return type for now):</p>
    <p>class ZipCompression implements CompressionInterface<br>
      {<br>
          public function compress(string $data, int $level)<br>
          {<br>
              var_dump($level);<br>
          }<br>
      }</p>
    <p>new GzipCompression()-&gt;compress('', default ?? 6);<br>
      new ZipCompression()-&gt;compress('', default ?? 6);<br>
    </p>
    <p>In this case, we get the following output:</p>
    <p>int(4)<br>
      Fatal error: Uncaught ValueError: Cannot pass default to required
      parameter 2 of ZipCompression::compress()</p>
    <p>I would like to fix this if possible, because I think this should
      be valid, with emphasis on <i>if possible</i>, because it may be
      prohibitively complex. Will update later.</p>
    <p>Cheers,<br>
      Bilge<br>
    </p>
  </body>
</html>

--------------LUUITnlHEQ15yUtwlHNJKF2r--