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Reply-To: Levi Morrison <levi.morrison@datadoghq.com>
Date: Fri, 16 Jun 2023 16:26:38 -0600
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To: Deleu <deleugyn@gmail.com>
Cc: PHP internals <internals@lists.php.net>
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Subject: Re: [PHP-DEV] [RFC] Interface Default Methods
From: internals@lists.php.net ("Levi Morrison via internals")

On Fri, Jun 16, 2023 at 11:51=E2=80=AFAM Deleu <deleugyn@gmail.com> wrote:
>
>
> On Thu, Jun 15, 2023 at 12:48=E2=80=AFAM Levi Morrison via internals <int=
ernals@lists.php.net> wrote:
>>
>> Hello, PHP Internals,
>>
>> I am moving my RFC for interface default methods to discussion:
>> https://wiki.php.net/rfc/interface-default-methods.
>>
>> This can be a useful tool for a few reasons:
>>  1. It can make implementing an interface easier when certain methods
>> can be implemented by other methods in the interface. For example, if
>> `Countable` had an `isEmpty(): bool` method, it could be implemented
>> by doing `$this->count() > 0`. Of course, if an implementation can be
>> more efficient, they are still free to implement it how they want.
>>  2. It can mitigate BC breaks in some cases. It's somewhat common for
>> authors to want to expand new methods onto existing interfaces over
>> time. Although this would still be a BC break, it moves it from a
>> massive change (every single implementor must add something, even if
>> it's a stub, or it will fail to compile) to a naming collision issue
>> only (only classes which already had a method of the same name will
>> fail to compile).
>>
>> There is prior art for this feature in both Java and C#. There may be
>> other languages, but I was aware of at least these.
>>
>> Note that the RFC links to a partial implementation. If there are two
>> or more interfaces with default methods of the same shape (name, args,
>> etc) and a class implements both interfaces and doesn't provide a
>> concrete implementation, which default implementation should be
>> chosen? There is a proposal for resolving this in some cases which is
>> modelled after Java's implementation, but it isn't implemented.
>>
>> Thank you for your time. I look forward to productive feedback.
>>
>> Levi Morrison
>>
>> --
>> PHP Internals - PHP Runtime Development Mailing List
>> To unsubscribe, visit: https://www.php.net/unsub.php
>>
>
> A question just occurred to me. Building up on the example of the RFC, is=
 the following snippet valid and would it behave as expected?
>
> ```
> interface Interface1 {
>     function method1() { echo __METHOD__ . "\n"; }
> }
>
> interface Interface2 {
>     function method1() { echo __METHOD__ . "\n"; }
> }
>
> class Class1 implements Interface1, Interface2 {
>     function method1() {
>         $result =3D Interface1::method1();
>
>         Interface2::method1();
>
>         return $result;
>     }
> }
>
> $result =3D (new Class1())->method1();
> ```
>
>
> --
> Marco Deleu

I'm not sure why you are saving `null` from `Interface1::method1()`'s
implicit return and then returning it from inside `Class1::method1`,
but yes, this is valid.