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Date: Mon, 27 Jan 2020 10:19:06 +0100
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To: Nicolas Grekas <nicolas.grekas+php@gmail.com>
Cc: PHP Internals List <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Adding a "Stringable" interface to PHP 8
From: nikita.ppv@gmail.com (Nikita Popov)

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On Wed, Jan 22, 2020 at 4:47 PM Nicolas Grekas <nicolas.grekas+php@gmail.com>
wrote:

> Hello everyone,
>
> as announced last week, I'm officially opening a discussion for adding a
> "Stringable" interface to PHP 8.
>
> The RFC and its rationale are presented here as required:
> https://wiki.php.net/rfc/stringable
>
> The patch is found on GitHub, where some discussions happened already, you
> might be interested in having a look:
> https://github.com/php/php-src/pull/5083
>
> TL;DR, I think we need an interface to allow passing objects with a
> __toString() method in a type-safe way, using the string|Stringable type.
> Here is the stub of the proposal:
> interface Stringable { public function __toString(): string; }
>
> I invite everyone to review the RFC before commenting here as I tried to
> sum up considerations that some already had before and that you might have
> too.
>
> Cheers,
> Nicolas
>

I'm wondering whether it could make sense to automatically implement this
interface for all classes that define __toString(). Explicitly implementing
the interface is useful for the transition period (where old PHP versions
also need to be supported), but when considering only PHP 8 support, I
think it may make sense to implicitly implement the interface. If the
__toString() functionality also works fine without implementing the
interface, and there's probably only going to be relatively few consumers
of the Stringable type, it will likely be quite common that the interface
will not get implemented...

Automatically implementing interfaces based on implemented methods could
also be a general language feature (see Go interfaces for example), but
likely not one we're interested in having in it's full generality. In this
particular case, it seems useful though.

Regards,
Nikita

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