With PHP we can define such variables whose values can not be changed after assigning. These varibles called CONSTANTS.
What is const?
Constants are one type of variable which we can define for any class with keyword const. Value of these variables can not be changed any how after assigning.
Class constants are diffrent than normal variables, as we do not need $ to declare the class constants. Values for the class constants can not be mathematical operation, function call, variable or property. It can have constant expression.
We can use these constants in interface also. If you are not sure what is Interface then you can refer this article for Interface in PHP.
If we are inside the class then values of the constants can be get using self keyword, but accessing the value outside the class you have to use Scope Resolution Operator ::.
If you access constant using class object and Arrow Operator ->, you will end up with Notice of Undefined Property.
const first_constant = "value of Constant";
const second_constant = 345;
// Inside Class self is used
echo self::first_constant . "\n";
echo self::second_constant . "\n";
// :: used to refer the Class Constants
echo example_class::first_constant . "\n";
$class = new example_class();
// Will print two Constants
// Shows Notice of Undefined Property
It will be better to use these Class Constants when you have variables with the fixed value, so It can not be changed further. Your suggestions?