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Date: Thu, 1 Mar 2018 23:04:18 +0000
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Subject: Re: [PHP-DEV] Traits with interfaces
From: rowan.collins@gmail.com (Rowan Collins)

Hi all,

On 01/03/2018 00:34, Marco Pivetta wrote:
>   - trait defined API can be imported with changed/aliased names, breaking
> therefore the contact defined in the interface

This isn't actually true, because trait method aliases create an *extra* 
copy of the pasted method, rather than actually renaming it. See example 
at the end of this e-mail for a demonstration.

I'm not sure why this is; the original traits RFC 
[https://wiki.php.net/rfc/horizontalreuse#renaming] says that it is 
because of "the dynamic nature of PHP", but the example it gives doesn't 
actually show anything breaking.

What *can* break an interface's contract is changing the *visibility* of 
the pasted method using "as protected" or "as private". This would need 
to be captured somehow while composing the class, probably producing a 
compile-time error, just as an explicit "implements" declaration would.

While looking for the above RFC, I came across this draft by Kevin 
Gessner from 2 years ago for exactly the feature discussed here: 
https://wiki.php.net/rfc/traits-with-interfaces It includes references 
to potential uses of this feature, and equivalents in other languages.

This appears to be the discussion in the archives, to avoid us repeating 
ourselves: https://marc.info/?t=145571923500003&r=1&w=2 and 
https://marc.info/?t=145573610000001&r=1&w=2


Appendix: Example of a trait providing implementation for an interface, 
even though the method was aliased:

# https://3v4l.org/DMAoY

interface Bobbable {
     public function bob();
}
trait Bobber {
     public function bob() {
         echo "Bobbity";
     }
}
class Bibble implements Bobbable {
     use Bobber { bob as bib; }
}
$b = new Bibble;
$b->bob();
$b->bib();


Regards,

-- 
Rowan Collins
[IMSoP]