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Date: Wed, 10 Nov 2021 16:12:54 -0500
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To: Nikita Popov <nikita.ppv@gmail.com>
Cc: PHP Internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] Automatic implementation of Stringable may conflict
 with old, untyped arginfo declarations
From: jmikola@gmail.com (Jeremy Mikola)

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On Tue, Nov 9, 2021 at 4:30 AM Nikita Popov <nikita.ppv@gmail.com> wrote:

>
> In
> https://github.com/php/php-src/commit/a551b083073ea08f8fc53b0e1a6380b6de26cc6b
> I've added a hack to add the string return type if it is missing and thus
> make the signature compatible with the interface. That should address the
> immediate compatibility issue.
>

Thanks for the quick fix.

A related question that came up, and is most likely unique to ext-mongodb,
follows. Many of our classes with toString() methods also implement a
corresponding interface with a toString() method. For example:

 * https://www.php.net/manual/en/class.mongodb-bson-binary.php
 * https://www.php.net/manual/en/class.mongodb-bson-binaryinterface.php

I'm in the process of adding explicit return type info to _all_ of our
toString() arginfos (classes and interfaces), but a thought occurred to me
that doing so may be a subtle BC break for userland classes implementing
these interfaces, since an explicit string return type would then become
necessary. But if I only modify our classes and leave our interfaces as-is,
PHP rightfully reports an error because the class' toString() method cannot
conform to both Stringable (with type info) and our interface (without type
info) -- at least PHP versions before 8.1.0RC6.

Reading the patch above, it looks like the automatic Stringable
implementation only kicks in when the arginfo has no existing return type
info. In that case, I think the only option to completely avoid a BC break
would be to continue to leave our return type info omitted (on both our
classes _and_ interfaces) and allow PHP 8.1+ to apply it automatically. Is
that correct?

-- 
jeremy mikola

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