Differences from objects
Although Enums are built on classes and objects, they do not support all object-related functionality. In particular, Enum cases are forbidden from having state.
- Constructors and Destructors are forbidden.
- Inheritance is not supported. Enums may not extend or be extended.
- Static or object properties are not allowed.
- Cloning an Enum case is not supported, as cases must be singleton instances.
- Magic methods, except for those listed below, are disallowed.
- Enums must always be declared before they are used.
The following object functionality is available, and behaves just as it does on any other object:
- Public, private, and protected methods.
- Public, private, and protected static methods.
- Public, private, and protected constants.
- Enums may implement any number of interfaces.
-
Enums and cases may have attributes attached
to them. The
TARGET_CLASStarget filter includes Enums themselves. TheTARGET_CLASS_CONSTtarget filter includes Enum Cases. - __call, __callStatic, and __invoke magic methods
__CLASS__and__FUNCTION__constants behave as normal
The ::class magic constant on an Enum type evaluates to the type
name including any namespace, exactly the same as an object. The ::class
magic constant on a Case instance also evaluates to the Enum type, as it is an
instance of that type.
Additionally, enum cases may not be instantiated directly with new, nor with
ReflectionClass::newInstanceWithoutConstructor() in reflection. Both will result in an error.
<?php
$clovers = new Suit();
// Error: Cannot instantiate enum Suit
$horseshoes = (new ReflectionClass(Suit::class))->newInstanceWithoutConstructor()
// Error: Cannot instantiate enum Suit
?>
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