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PHP Class Constants

PHP Class Constants

What you'll learn

  • Understand the main ideas in PHP Class Constants.
  • See a working example and explanation to help you learn by doing.
  • Follow a clear path to the next lesson in this topic.

When to use this lesson

Use this lesson when you want to understand the key concepts behind PHP Class Constants.

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PHP Class Constants

Constants cannot be changed once they are declared. If you need to define some constant data within a class, a Class Constant is what you are looking for.

Class constants can be useful if you need to define settings, states, or warning messages that belong to a class and should remain fixed.

Defining and Accessing a Constant

A class constant is declared inside a class with the const keyword. By default, they are highly accessible.

Class constants are completely different from regular variables. We do not use the $ symbol to declare or access them, and we do not use the $this keyword or the -> operator.

Instead, we use the Scope Resolution Operator (::).

Class Constant Example

<?php
class Goodbye {
  const LEAVING_MESSAGE = "Thank you for visiting IntricateDevo!";
  

  public function byebye() {
    // Accessing a constant from INSIDE the class uses self::
    echo self::LEAVING_MESSAGE;
  }
}


// Accessing a constant from OUTSIDE the class uses ClassName::
echo Goodbye::LEAVING_MESSAGE;
echo "\n";


$obj = new Goodbye();
$obj->byebye();
?>

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