PHP: rfc:php-namespace-in-core

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====== PHP RFC: PHP Namespace in core ======
  * Version: 1.2.0
  * Date: 2020-03-25
  * Author: Michał Brzuchalski <brzuchal@php.net>, George Peter Banyard <girgias@php.net>
  * Status: Declined
  * First Published at: http://wiki.php.net/rfc/php-namespace-in-core

===== Introduction =====
The PHP project has reserved the right to use the ''\PHP'' namespace but has never acted upon starting to use it. We therefore propose that core symbols which cannot be unbundled such as those related to the language/parser/interpreter must use ''\PHP'' namespace.

This paves the way to reduce the usage of the global namespace as "PHP"'s namespace.

This is not a concrete proposal on how to structure the namespace or a proposal on re-aliasing classes to use the ''\PHP'' namespace. This is only an agreement that core classes or newly introduced symbols which are tightly coupled to the PHP engine must start using the ''\PHP'' namespace, e.g. for type prefixes.

===== Features which could benefit from the PHP namespace =====

  * The recently accepted [[rfc:token_as_object|PHP RFC: Object-based token_get_all() alternative]] uses the <php>\PhpToken</php> class but under this proposal it could be <php>\PHP\PhpToken</php>
  * The currently under discussion [[rfc:attributes_v2|PHP RFC: Attributes v2]] could use the ''\PHP'' namespace for engine/internal related attributes.

As these sort of symbols are tied to the engine there is no risk that they will get unbundled from PHP core and moved to PECL. We note this as we are aware that if a non core extension would use the ''\PHP'' namespace and gets unbundled and moved to PECL we would find ourselves in a situation where symbols under the ''\PHP'' namespace are not always available in PHP.

==== A small concrete example ====
Currently <php>debug_backtrace()</php> produces an array of arrays. An object oriented API could introduce the <php>Frame</php> class to hold details about each frame in the backtrace. As this would be an internal API using the ''\PHP'' namespace signals clear ownership and possibly limit the BC breaks for users which don't use the namespace feature of PHP.

===== Proposal =====
New features or symbols which are tightly coupled to the internals/engine of the PHP interpreter must use the ''\PHP'' namespace starting from PHP 8.

===== Backward Incompatible Changes =====
No backwards incompatible changes as only new classes/symbols would be introduces under the ''\PHP'' namespace.

===== Proposed PHP Version =====
PHP 8.0.

===== Concerns about inconsistent use =====
Various symbols which are widely used are located in the global namespace, classes such as ''Closure'' or ''Generator'' and interfaces such as ''Countable'', ''ArrayAccess'', and many others.

Although some of these fall into the category of being tightly tied to the engine and would land in the ''\PHP'' namespace under this proposal if newly introduced. We consider the long term advantage of using the namespace and the benefits it can provide as a an acceptable trade-off.

===== Future scope =====
Providing new core APIs building on new features introduces in PHP, such as:

  * I/O API using exceptions instead of warnings in case of failure
  * New data structures to replace SPL data structures, see Appendix for reasons why

Or revamping current ones:
  
  * Reflection, see Appendix for a use case 
 
===== Proposed Voting Choices =====
The vote is a straight Yes/No vote requiring a 2/3 majority to accept the RFC.

===== Vote =====
Voting started on 2020-05-22 and will end on 2020-06-04 at 6:00 UTC.
<doodle title="Accept PHP namespace in core RFC?" auth="brzuchal" voteType="single" closed="true">
   * Yes
   * No
</doodle>

===== Patches and Tests =====
This RFC doesn't provide any changes.

===== Changelog =====
1.0.0: Initial version \\
1.1.0: New features must use the PHP engine, before this was merely a suggestion \\
1.2.0: Major rewrite, addressing concerns about inconsistent usage \\

===== Appendix =====
==== SPL Data Structures ====
An infamous example is that <php> SplQueue extends SplDoublyLinkedList</php> meaning <php>SplQueue</php> inherits the <php>push()</php> and <php>pop()</php> methods from <php>SplDoublyLinkedList</php>.

Therefore, if a user decides to use these methods instead of the designated <php>enqueue()</php> and <php>dequeue()</php> methods the behaviour obtained is the one of a stack instead of a queue.

==== Reflection ====
Currently within the Reflection extension we have the following classes ''ReflectionType'' and ''ReflectionNamedType'' however their purpose isn't exactly to present a type.

From PHP's type system perspective, a class is a type. Therefore, ''ReflectionClass'' not extending from ''ReflectionType'' could be seen as questionable. Thus the ''ReflectionType'' class acts more as a type constraint and renaming it to ''ReflectionTypeConstraint'' may be a good way to clarify it's concern.

Thus, in a revamped Reflection extension one could imagine a more accurate ''PHP\ReflectionTypeConstraint'' to represent the current ''ReflectionType'' and introduce a new top reflector ''PHP\ReflectionType'' for all types current, and future. E.g Enums, Generics, etc.
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