define() vs const in PHP

Lets understand on difference between define() vs const in php.

In PHP, both define() and const are used to define constants, but they have some differences in terms of their usage and behavior.

  1. Syntax:
    • define() is a function that takes two parameters: the constant name as a string and its value. For example: define('MY_CONSTANT', 10);.
    • const is a language construct that is used to define constants within a class or at the global level. It does not require parentheses. For example: const MY_CONSTANT = 10;.
  2. Usage:
    • define() can be used both inside and outside of classes and functions. It allows dynamic constant names and values since it is a function call.
    • const can only be used within classes or at the global level. It requires static values, meaning you can only assign constant expressions and literals. You cannot use variables or function calls to define const.
  3. Scope:
    • define() constants have global scope by default. They can be accessed anywhere in the code, even within functions or classes.
    • const constants have different scopes depending on where they are defined. If defined within a class, they have class scope and can be accessed using the class name. If defined outside a class, they have global scope.
  4. Performance:
    • const constants are resolved at compile-time and are generally faster because they are resolved directly by the PHP engine.
    • define() constants are resolved at runtime since they are function calls, which can have a slight impact on performance.
  5. Conditional Usage:
    • define() allows conditional definitions. You can use it inside control structures or functions to conditionally define constants based on runtime conditions.
    • const does not allow conditional definitions. Constants defined with const are determined at compile-time and cannot be changed or redefined during runtime.

In general, if you are defining constants that don’t need to change and have static values, it’s recommended to use const for better performance. If you need dynamic constant names or values or conditional definitions, then define() is the appropriate choice.

That’s it on difference between define() vs const in php.