Dynamic Constant¶
A constant is dynamic when its name is in a variable, or another container, and is accessed at execution time.
Reaching a constant’s value is done by using the constant() function, or the dynamic constant fetch with classes.
Sometimes, dynamic constants are also called variable constants.
<?php
const A = 1;
// simple case
$a = 'A';
echo constant($a); // displays 1
// with leading backslash
$b = '\A';
echo constant($b); // displays 1
// definition has no leading backslash
define('B\C', d);
// reading has no leading backslash, or not
$c = '\b\C';
echo constant($c); // displays d
$c = 'b\C';
echo constant($c); // displays d
// constant() works also on class constants.
class D {
const E = 'f';
}
echo constant('d::E'); // displays f
// dynamic constant access on classes or enumeration
$k = 'E';
echo D::{$k}; // f
// constant works also on enumeration cases
enum I: string {
case G = 'h';
}
echo constant('I::G')->value; // displays h
// dynamic constant access on classes or enumeration
$g = 'G';
echo I::{$g}->value; // h
?>
See also All the Dynamic Syntax in PHP.
Related : Constants, constant(), Class Constant Syntax, Static Constant, Dynamic
