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Date: Fri, 27 Aug 2021 22:07:20 +0100
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Subject: Re: [PHP-DEV] Make namespace part of runtime
From: rowan.collins@gmail.com (Rowan Tommins)

On 27/08/2021 20:47, Olle Härstedt wrote:
> As a followup for my previous post, I think this could be a good place
> to start to enable attribute writers to create encapsulation mechanics
> for composition, like namespace visibility, "internal" access or
> friend classes.


In my experience PHP projects tend to use namespace hierarchies which 
are deep rather than broad, and I'm not sure how easily those 
hierarchies could be re-purposed as scopes.

Clicking through the Symfony source at random for an example, I found 
"namespace 
Symfony\Component\Messenger\Transport\Serialization\Normalizer", which 
contains only one class.

A trivial implementation of namespace visibility which just matched the 
exact namespace string would be completely useless for that class (it 
would be the same as "private"). A slightly less trivial 
implementationmight allow access from "child namespaces", but that 
wouldn't help in this case.

However, it might be really useful to restrict usage of that class, or 
some of its members, to classes in the "Symfony\Component\Messenger" 
namespace; or maybe to those in the 
"Symfony\Component\Messenger\Transport\Serialization" namespace.

I can see two ways of enabling that:

- Allowing visibility modifiers to specify exactly what level of prefix 
they refer to. This is apparently how Scala approaches things, allowing 
you to write the equivalent of "private[Symfony\Component\Messenger] 
$foo; protected[Symfony\Component\Messenger\Transport\Serialization] $bar;"

- Introducing a separate concept of "package", either orthogonal to 
namespaces or overlapping with them, e.g. "package 
Symfony\Component\Messenger; namespace 
Transport\Serialization\Normalizer;" would still give a class name 
beginning 
"Symfony\Component\Messenger\Transport\Serialization\Normalizer", but 
would define "internal" to mean accessible within the 
"Symfony\Component\Messenger" package.


I'm personally quite keen on the idea of packages, because they're how a 
lot of PHP code is developed in practice - as modular libraries linked 
by Composer - and I think we could optimise the language for that use 
(e.g. applying more cross-file optimisations within a fully preloaded 
package).


Regards,

-- 
Rowan Tommins
[IMSoP]