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| Constants |
Constants
Constants are a type of variable in PHP. The define() function to set a constant takes three arguments - the key name, the key's value, and a Boolean (true or false) which determines whether the key's name is case-insensitive (false by default). A constant's value cannot be altered once it is set. It is used for values which rarely change (for example a database password OR api key).
Scope
It is important to know that unlike variables, constants ALWAYS have a global scope and can be accessed from any function in the script.
Example
<?php
define("freeCodeCamp", "Learn to code and help nonprofits", false);
echo freeCodeCamp;
Output:
Learn to code and help nonprofits
Also, when you are creating classes, you can declare your own constants.
class Human {
const TYPE_MALE = 'm';
const TYPE_FEMALE = 'f';
const TYPE_UNKNOWN = 'u'; // When user didn't select his gender
.............
}
Note: If you want to use those constants inside the Human class, you can refer them as self::CONSTANT_NAME. If you want to use them outside the class, you need to refer them as Human::CONSTANT_NAME.