Sean Coates


Reeze Xia


PHP RFC: Support Class Constant Visibility


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. 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.


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:

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();

Backward Incompatible Changes

Proposed PHP Version(s)

This RFC targets PHP 7.1

RFC Impact



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.

Patches and Tests

A pull request has been made. It is feature complete but needs review, more tests, and help with opcache changes :

This feature was merged into PHP master here:



Version Changed Date
0.2 Implemented
0.1 Initial version


An option needs 2/3 votes to win

Class Constant Visibility (93.3% approved)
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