PHP: rfc:class_const_visibility

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====== PHP RFC: Support Class Constant Visibility ======
  * Version: 0.2
  * Date: 2015-09-13
  * Author: Sean DuBois <sean@siobud.com>, Reeze Xia <reeze@php.net>
  * Status: Implemented
  * First Published at: http://wiki.php.net/rfc/class_const_visibility


===== Introduction =====

Classes in PHP allow modifiers on properties and methods, but not constants.
It is an easily fixed inconsistency, and a feature that many want and most surprised
that it doesn't already exist.  [[http://stackoverflow.com/questions/5339456/php-class-constant-visibility|Stack Overflow Thread]]

In a thread on php-internals a couple real world examples were offered.
    * Defining bitmasks/magic numbers, but not exposing them globally. Before constants would be exposed allowing callers to depend on them.
    * Help make it more clear what is important, exposing harmless constants clutters documentation  needlessly. 

===== Proposal =====

This RFC propose PHP support class constant visibility that mirror the behavior of method
and property visibility. 

Class constant may be define as public, private or protected. class constants declared
without any explicit visibility keyword are defined as public. 

Proposed syntax:

<code php>
<?php

class Token {
	// Constants default to public
	const PUBLIC_CONST = 0;

        // Constants then also can have a defined visibility
        private const PRIVATE_CONST = 0;
        protected const PROTECTED_CONST = 0;
        public const PUBLIC_CONST_TWO = 0;
        
        //Constants can only have one visibility declaration list
        private const FOO = 1, BAR = 2;
}


//Interfaces only support public consts, and a compile time error will be thrown for anything else. Mirroring the behavior of methods.
interface ICache {
        public const PUBLIC = 0;
        const IMPLICIT_PUBLIC = 1;
}

//Reflection was enhanced to allow fetching more than just the values of constants
class testClass  {
  const TEST_CONST = 'test';
}

$obj = new ReflectionClass( "testClass" );
$const = $obj->getReflectionConstant( "TEST_CONST" );
$consts = $obj->getReflectionConstants();

</code>


===== Backward Incompatible Changes =====

===== Proposed PHP Version(s) =====

This RFC targets PHP 7.1

===== RFC Impact =====

==== To SAPIs ====

None.

==== To Existing Extensions ====

None, all the class constant APIs will be the same.
There will be new _ex APIs that allow callers to explicitly pass flags.

If a extension accesses non-public structures (the now non-existent class_constants HashTable) there will be breakage

==== To Opcache ====

Need update.

===== Vote =====

Simple Yes/No option. This requires a 2/3  majority.

This vote will close on 06:00 UTC on Tuesday 2015-10-27

<doodle title="Class Constant Visibility" auth="sdubois" voteType="single" closed="true">
   * Yes
   * No
</doodle>

===== Patches and Tests =====

A pull request has been made. It is feature complete but needs review, more tests, and help with opcache changes : https://github.com/php/php-src/pull/1494

This feature was merged into PHP master here: https://github.com/php/php-src/commit/a75c195000b3226904103244fa9c3d0ce1111838

===== References =====
  * http://php.net/manual/en/language.oop5.constants.php
  * http://php.net/manual/en/language.oop5.visibility.php

===== Changelog =====

  * V0.1 Initial version
  * V0.2 Adopted by Sean DuBois <sean@siobud.com>
  * V0.2 Implemented
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