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 default visibility of class constants is public.
The value must be a constant expression, not (for example) a variable, a property, or a function call.
It’s also possible for interfaces to have constants. Look at the interface documentation for examples.
As of PHP 5.3.0, it’s possible to reference the class using a variable. The variable’s value can not be a keyword (e.g. self, parent and static).
Example #1 Defining and using a constant
1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 | <?php class MyClass { const CONSTANT = 'constant value'; function showConstant() { echo self::CONSTANT . "\n"; } } echo MyClass::CONSTANT . "\n"; $classname = "MyClass"; echo $classname::CONSTANT . "\n"; // As of PHP 5.3.0 $class = new MyClass(); $class->showConstant(); echo $class::CONSTANT."\n"; // As of PHP 5.3.0 ?> |
Example #2 Static data example
1 2 3 4 5 6 7 8 9 10 11 12 | <?php class foo { // As of PHP 5.3.0 const BAR = <<<'EOT' bar EOT; // As of PHP 5.3.0 const BAZ = <<<EOT baz EOT; } ?> |
Reference: https://www.php.net/manual/en/language.oop5.constants.php
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