Use Const
December 18, 2014 ยท View on GitHub
There are two ways to create constants in PHP : const and define.
const may be used to create constants. Those constants will be placed the current namespace. Since PHP 5.6, static constant expressions may be used, giving some flexibility on constant creation. When not used in a class, const must be used at the top level of a namespace : no function, class, nor if..then or any loop structure. All has to be known at compile time. This may give const its main advantages : it is slightly faster and more readable than its counterpart, define.
define, on the other hand, is the time-honored function to create constants. It may be used to create constants anywhere in the code, with dynamical expressions or not. The resulting constant will be available in the global space, or in the namespace if the namespace was included in the constant name at definition time. It may also be made case insensitive.
define tends to be slower that const, and will not benefit much from opcode cache. This will be specially visible when using large number of constants.
It is recommended to use const whenever possible.
Rule Details
The following are considered a warning :
<?php
define('a', 1);
define('b', 'a' . 'c');
define('c', someClass::constant);
?>
The following are OK :
<?php
define('l', 3, true);
define('m', $x, true);
define('n', array(1,2,3), true); // before PHP 5.6
?>
When Not To Use It
For backward compatibility, or to load configuration as constants, define() is still more convenient for definition. In terms of usage, both syntax are good.