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Date: Sun, 2 Jul 2023 20:43:27 -0600
Message-ID: <CAFMT4NojV3yJZbPvss3Jo3ch8ULaHHCL1c9O_wYvfkHFiqjcBA@mail.gmail.com>
To: Ben Ramsey <ben@benramsey.com>
Cc: internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [VOTE] Interface Default Methods
From: morrison.levi@gmail.com (Levi Morrison)

On Sun, Jul 2, 2023 at 7:08=E2=80=AFPM Ben Ramsey <ben@benramsey.com> wrote=
:
>
> On Jul 2, 2023, at 19:11, Levi Morrison <morrison.levi@gmail.com> wrote:
>
> =EF=BB=BFChatter on the [Interface Default Methods RFC][1] has been quiet=
 for
> the past 6 days, and the feature freeze deadline is fast approaching
> for PHP 8.3, so I'm moving this to vote. It'll be open for two weeks
> as usual.
>
> Thanks to everyone who discussed weaknesses in the RFC during the
> discussion phase.
>
>  [1]: https://wiki.php.net/rfc/interface-default-methods
>
>
>
> I=E2=80=99m probably going to vote =E2=80=9Cyes=E2=80=9D on this, but sin=
ce the property accessors RFC won=E2=80=99t be ready for 8.3,[1] and that R=
FC covers use of properties in interfaces, how useful will interface defaul=
t methods be without interface properties?

Plenty useful, I think. Interfaces deal with abstractions, so there
are often things you can do without having state. Java's interfaces
don't allow properties, for instance, and they still have this
feature.

As an example, this poor-man Sequence interface works, because the
behavior and state for `next` is provided by the implementer:

```php
<?php

interface Sequence {
    // return null to indicate the end of sequence
    function next();

    function fold($initial, callable $f) {
        $reduction =3D $initial;
        while (($next =3D $this->next()) !=3D=3D null) {
            $reduction =3D $f($reduction, $next);
        }
        return $reduction;
    }

    function reduce(callable $f) {
        $next =3D $this->next();
        return $next !=3D=3D null
            ? $this->fold($next, $f)
            : null;
    }

    function into_array_list(): array {
        $array =3D [];
        while (($next =3D $this->next()) !=3D=3D null) {
            $array[] =3D $next;
        }
        return $array;
    }
}

final class IteratorSequence
    implements Sequence
{
    function __construct(private Iterator $iter) {
        $this->iter->rewind();
    }

    function next() {
        $iter =3D $this->iter;
        if ($iter->valid()) {
            $next =3D $iter->current();
            $iter->next();
            return $next;
        }
        return null;
    }
}

function xrange($begin, $end) {
    $i =3D $begin;
    while ($i < $end) {
        yield $i++;
    }
}

$seq =3D new IteratorSequence(xrange(1, 10));
var_export($seq->into_array_list());
echo PHP_EOL;
```