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. Like
static members, constant values
cannot be accessed from an instance of the object (using
$object::constant).
The value must be a constant expression, not (for example) a variable, a
class member, result of a mathematical operation or a function call.
Example 19-17. Defining and using a constant
<?php
class MyClass
{
const constant = 'constant value';
function showConstant() {
echo self::constant . "\n";
}
}
echo MyClass::constant . "\n";
$class = new MyClass();
$class->showConstant();
// echo $class::constant; is not allowed
?>
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