Class constant in PHP

Class constant in PHP, is a constant declared inside class which value cannot be changed once assigned.

1. const keyword is used to declare class constant.
2. $ symbol is not used before const variable.
3. Class constant variable name must be in uppercase as per naming convention.
4. Class constant variable names are case-sensitive.

Syntax

<?php

 class classname{
   const variable_name = value;
 }

?>

Example

<?php
 class myClass{
    const MAX_SPEED = 200;
 }
?>

Access class constants

To access or use a class constant, scope resolution operator :: (double colon without space) is used with class name.

<?php
 class myClass{
    const MAX_SPEED = 200;
 }
// Accessing class constant
echo myClass::MAX_SPEED;
?>

Inside class function

PHP allows to use $this or self to access a class constant inside class methods.

 <?php
class myClass{
    const MAX_SPEED = 200;

    public function getSpeed(){
    // With $this
     echo $this::MAX_SPEED;
    // With self
     echo self::MAX_SPEED;
   }
 }
$obj = new myClass();
$obj->getSpeed();
?>