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Class Constants
It is possible to define constant values on a per-class basis remaining the
same and unchangeable. Constants differ from normal variables in that you
don't use the $ symbol to declare or use them.
The value must be a constant expression, not (for example) a variable, a class member, result of a mathematical operation or a function call.
As of PHP 5.3.0, it's possible to reference the class using a variable.
Keywords like self, parent or
static are not allowed in dynamic class references.
Example 10.17. Defining and using a constant
<?php
class MyClass
{
const constant = 'constant value';
function showConstant() {
echo self::constant . "\n";
}
}
echo MyClass::constant . "\n";
$classname = "MyClass";
echo $classname::constant . "\n";
$class = new MyClass();
$class->showConstant();
echo $class::constant."\n";
?>