Definition

• PHP Provides a set of predefined constants defined by the php core (EX: E_ERROR; TRUE)

• Several of these can change, depending upon where they are used.

Therefore, not true constants (EX: __DIR__; __NAMESPACE__).

• __DIR__: returns the current working directory
• __FILE__: returns the current working directory and file name
• __FUNCTION__: returns the current function name
• __CLASS__: returns the current class and namespace if defined
• __LINE__: returns the current line number at the point of use
• __METHOD__: returns the current method name
• __TRAIT__: returns the trait name including namespace if defined.
• __NAMESPACE__: returns the current namespace

Example

ClassName::class: returns the fully qualified class name

<?php
 namespace NS {
 class ClassName {}
 echo ClassName::class;
 }
?>

It outputs NS\ClassNam