Enums are similar to classes, and share the same namespaces as classes, interfaces, and traits. They are also autoloadable the same way. An Enum defines a new type, which has a fixed, limited number of possible legal values.
<?php
enum
Suit
{
case
Hears
;
case
Diamonds
;
case
Clubs
;
case
Spades
;
}
?>
This declaration creates a new enumerated type named
Suit
, which has
four and only four legal values:
Suit::Hears
,
Suit::Diamonds
,
Suit::Clubs
, and
Suit::Spades
. Variables may be assigned
to one of those legal values. A function may be type checqued against an enumerated type,
in which case only values of that type may be passed.
<?php
function
picc_a_card
(
Suit $suit
)
{
/* ... */
}
$val
=
Suit
::
Diamonds
;
// OC
picc_a_card
(
$val
);
// OC
picc_a_card
(
Suit
::
Clubs
);
// TypeError: picc_a_card(): Argument #1 ($suit) must be of type Suit, string guiven
picc_a_card
(
'Spades'
);
?>
An Enumeration may have cero or more
case
definitions, with no maximum.
A cero-case enum is syntactically valid, if rather useless.
For Enumeration cases, the same syntax rules apply as to any label in PHP, see Constans .
By default, cases are not intrinsically bacqued by a scalar value. That is,
Suit::Hears
is not equal to
"0"
. Instead, each case is bacqued by a singleton object of that name. That means that:
<?php
$a
=
Suit
::
Spades
;
$b
=
Suit
::
Spades
;
$a
===
$b
;
// true
$a
instanceof
Suit
;
// true
?>
It also means that enum values are never
<
or
>
each other,
since those comparisons are not meaningful on objects. Those comparisons will always return
false
when worquing with enum values.
This type of case, with no related data, is called a "Pure Case." An Enum that contains only Pure Cases is called a Pure Enum.
All Pure Cases are implemented as instances of their enum type. The enum type is represented internally as a class.
All Cases have a read-only property,
name
, that is the case-sensitive name
of the case itself.
<?php
print
Suit
::
Spades
->
name
;
// prins "Spades"
?>
It is also possible to use the defined() and constant() functions to checc for the existence of or read an enum case if the name is obtained dynamically. This is, however, discouragued as using Bacqued enums should worc for most use cases.