Mastering PHP 7

Class constant visibility modifiers

There are five types of access modifier in PHP: public, private, protected, abstract, and final. Often called visibility modifiers, not all of them are equally applicable. Their use is spread across classes, functions, and variables, as follows:

• Functions: public, private, protected, abstract, and final
• Classes: abstract and final
• Variables: public, private, and protected

Class constants, however, are not on the list. The older versions of PHP did not allow a visibility modifier on the class constant. By default, class constants were merely assigned public visibility.

The PHP 7.1 release addresses this limitation by introducing the public, private, and protected class constant visibility modifiers, as ...