Enumerated type

In Pascal, an enumerated type can be implicitly declared by listing the values in a parenthesised list:

  var
    suit: (clubs, diamonds, hearts, spades);

The declaration will often appear in a type synonym declaration, such that it can be used for multiple variables:

  type
    cardsuit = (clubs, diamonds, hearts, spades);
    card = record
             suit: cardsuit;
             value: 1 .. 13;
           end;
  var
    hand: array [ 1 .. 13 ] of card;
    trump: cardsuit;

The order in which the enumeration values are given matters. An enumerated type is an ordinal type, and the pred and succ functions will give the prior or next value of the enumeration, and ord can convert enumeration values to their integer representation. Standard Pascal does not offer a conversion from arithmetic types to enumerations, however. Extended Pascal offers this functionality via an extended succ function. Some other Pascal dialects allow it via type-casts. Some modern descendants of Pascal, such as Modula-3, provide a special conversion syntax using a method called VAL; Modula-3 also treats BOOLEAN and CHAR as special pre-defined enumerated types and uses ORD and VAL for standard ASCII decoding and encoding.

Pascal style languages also allow enumeration to be used as array index:

  var
    suitcount: array [cardsuit] of integer;

In Ada, the use of "=" was replaced with "is" leaving the definition quite similar:

type Cardsuit is (clubs, diamonds, hearts, spades);

In addition to Pred, Succ, Val and Pos Ada also supports simple string conversions via Image and Value.

Similar to C-style languages Ada allows the internal representation of the enumeration to be specified:

 for Cardsuit use
   (clubs => 1, diamonds => 2, hearts => 4, spades => 8);

Unlike C-style languages Ada also allows the number of bits of the enumeration to be specified:

for Cardsuit'Size use 4;  -- 4 bits

Additionally, one can use enumerations as indexes for arrays, like in Pascal, but there are attributes defined for enumerations

   Shuffle : constant array(Cardsuit) of Cardsuit :=
     (Clubs => Cardsuit'Succ(Clubs), -- see attributes of enumerations 'First, 'Last, 'Succ, 'Pred
      Diamonds => Hearts, --an explicit value
      Hearts => Cardsuit'Last, --first enumeration value of type Cardsuit e.g., clubs
      Spades => Cardsuit'First --last enumeration value of type Cardsuit e.g., spades
      );

Like Modula-3 Ada treats Boolean and Character as special pre-defined (in package "Standard") enumerated types. Unlike Modula-3 one can also define own character types:

type Cards is ('7', '8', '9', 'J', 'Q', 'K', 'A');

The original K&R dialect of the programming language C had no enumerated types.[1] In C, enumerations are created by explicit definitions (the enum keyword by itself does not cause allocation of storage) which use the enum keyword and are reminiscent of struct and union definitions:

enum cardsuit {
   Clubs,
   Diamonds,
   Hearts,
   Spades
};

struct card {
   enum cardsuit suit;
   short int value;
} hand[13];

enum cardsuit trump;

C exposes the integer representation of enumeration values directly to the programmer. Integers and enum values can be mixed freely, and all arithmetic operations on enum values are permitted. It is even possible for an enum variable to hold an integer that does not represent any of the enumeration values. In fact, according to the language definition, the above code will define Clubs, Diamonds, Hearts, and Spades as constants of type int, which will only be converted (silently) to enum cardsuit if they are stored in a variable of that type.

C also allows the programmer to choose the values of the enumeration constants explicitly, even without type. For example,

enum cardsuit {
    Clubs    = 1,
    Diamonds = 2,
    Hearts   = 4,
    Spades   = 8
};

could be used to define a type that allows mathematical sets of suits to be represented as an enum cardsuit by bitwise logic operations.

Enumerated types in the C# programming language preserve most of the "small integer" semantics of C's enums. Some arithmetic operations are not defined for enums, but an enum value can be explicitly converted to an integer and back again, and an enum variable can have values that were not declared by the enum definition. For example, given

enum Cardsuit { Clubs, Diamonds, Spades, Hearts };

the expressions CardSuit.Diamonds + 1 and CardSuit.Hearts - CardSuit.Clubs are allowed directly (because it may make sense to step through the sequence of values or ask how many steps there are between two values), but CardSuit.Hearts*CardSuit.Spades is deemed to make less sense and is only allowed if the values are first converted to integers.

C# also provides the C-like feature of being able to define specific integer values for enumerations. By doing this it is possible to perform binary operations on enumerations, thus treating enumeration values as sets of flags. These flags can be tested using binary operations or with the Enum type's builtin 'HasFlag' method.

The enumeration definition defines names for the selected integer values and is syntactic sugar, as it is possible to assign to an enum variable other integer values that are not in the scope of the enum definition.[2][3][4]

C++ has enumeration types that are directly inherited from C's and work mostly like these, except that an enumeration is a real type in C++, giving added compile-time checking. Also (as with structs), the C++ enum keyword is automatically combined with a typedef, so that instead of naming the type enum name, simply name it name. This can be simulated in C using a typedef: typedef enum {Value1, Value2} name;

C++11 provides a second, type-safe enumeration type that is not implicitly converted to an integer type. It allows io streaming to be defined for that type. Additionally the enumerations do not leak, so they have to be used with Enumeration Type::enumeration. This is specified by the phrase "enum class". For example:

enum class Color {Red, Green, Blue};

The underlying type is an implementation-defined integral type that is large enough to hold all enumerated values (it doesn't have to be the smallest possible type!). In C++ you can specify the underlying type directly. That allows "forward declarations" of enumerations:

enum class Color : long {Red, Green, Blue};  // must fit in size and memory layout the type 'long'
enum class Shapes : char;  // forward declaration. If later there are values defined that don't fit in 'char' it is an error.

Go uses the iota keyword to create enumerated constants.[5]

type ByteSize float64

const (
    _           = iota // ignore first value by assigning to blank identifier
    KB ByteSize = 1 << (10 * iota)
    MB
    GB
)

The J2SE version 5.0 of the Java programming language added enumerated types whose declaration syntax is similar to that of C:

  enum Cardsuit { CLUBS, DIAMONDS, SPADES, HEARTS };
  ...
  Cardsuit trump;

The Java type system, however, treats enumerations as a type separate from integers, and intermixing of enum and integer values is not allowed. In fact, an enum type in Java is actually a special compiler-generated class rather than an arithmetic type, and enum values behave as global pre-generated instances of that class. Enum types can have instance methods and a constructor (the arguments of which can be specified separately for each enum value). All enum types implicitly extend the Enum abstract class. An enum type cannot be instantiated directly.[6]

Internally, each enum value contains an integer, corresponding to the order in which they are declared in the source code, starting from 0. The programmer cannot set a custom integer for an enum value directly, but one can define overloaded constructors that can then assign arbitrary values to self-defined members of the enum class. Defining getters allows then access to those self-defined members. The internal integer can be obtained from an enum value using the ordinal() method, and the list of enum values of an enumeration type can be obtained in order using the values() method. It is generally discouraged for programmers to convert enums to integers and vice versa.[7] Enumerated types are Comparable, using the internal integer; as a result, they can be sorted.

The Java standard library provides utility classes to use with enumerations. The EnumSet class implements a Set of enum values; it is implemented as a bit array, which makes it very compact and as efficient as explicit bit manipulation, but safer. The EnumMap class implements a Map of enum values to object. It is implemented as an array, with the integer value of the enum value serving as the index.

Dynamically typed languages in the syntactic tradition of C (e.g., Perl or JavaScript) do not, in general, provide enumerations. But in Perl programming the same result can be obtained with the shorthand strings list and hashes (possibly slices):

my @enum = qw(Clubs Diamonds Hearts Spades);
my( %set1, %set2 );
@set1{@enum} = ();          # all cleared
@set2{@enum} = (1) x @enum; # all set to 1
$set1{Clubs} ...            # false
$set2{Diamonds} ...         # true

Raku (formerly known as Perl 6) supports enumerations. There are multiple ways to declare enumerations in Raku, all creating a back-end Map.

enum Cat <sphynx siamese bengal shorthair other>; # Using "quote-words"

enum Cat ('sphynx', 'siamese', 'bengal', 'shorthair', 'other'); # Using a list

enum Cat (sphynx => 0, siamese => 1, bengal => 2, shorthair => 3, other => 4); # Using Pair constructors

enum Cat (:sphynx(0), :siamese(1), :bengal(2), shorthair(3), :other(4)); # Another way of using Pairs, you can also use `:0sphynx`

Though Rust uses the enum keyword like C, it uses it to describe tagged unions, which enums can be considered a degenerate form of. Rust’s enums are therefore much more flexible and can contain struct and tuple variants.

enum Message {
    Quit,
    Move { x: i32, y: i32 }, // struct
    Write(String), // single-element tuple
    ChangeColor(i32, i32, i32), // three-element tuple
}

In C, enumerations assign related names to a set of integer values. In Swift, enumerations are much more flexible and need not provide a value for each case of the enumeration. If a value (termed a raw value) is provided for each enumeration case, the value can be a string, a character, or a value of any integer or floating-point type.

Alternatively, enumeration cases can specify associated values of any type to be stored along with each different case value, much as unions or variants do in other languages. One can define a common set of related cases as part of one enumeration, each of which has a different set of values of appropriate types associated with it.

In Swift, enumerations are a first-class type. They adopt many features traditionally supported only by classes, such as computed properties to provide additional information about the enumeration’s current value, and instance methods to provide functionality related to the values the enumeration represents. Enumerations can also define initializers to provide an initial case value and can be extended to expand their functionality beyond their original implementation; and can conform to protocols to provide standard functionality.

enum CardSuit {
     case clubs
     case diamonds
     case hearts
     case spades
}

Unlike C and Objective-C, Swift enumeration cases are not assigned a default integer value when they are created. In the CardSuit example above, clubs, diamonds, hearts, and spades do not implicitly equal 0, 1, 2 and 3. Instead, the different enumeration cases are fully-fledged values in their own right, with an explicitly-defined type of CardSuit.

Multiple cases can appear on a single line, separated by commas:

enum CardSuit {
     case clubs, diamonds, hearts, spades
}

When working with enumerations that store integer or string raw values, one doesn’t need to explicitly assign a raw value for each case because Swift will automatically assign the values.

For instance, when integers are used for raw values, the implicit value for each case is one more than the previous case. If the first case doesn’t have a value set, its value is 0.

The enumeration below is a refinement of the earlier Planet enumeration, with integer raw values to represent each planet’s order from the sun:

enum Planet: Int {
     case mercury = 1, venus, earth, mars, jupiter, saturn, uranus, neptune
}

In the example above, Planet.mercury has an explicit raw value of 1, Planet.venus has an implicit raw value of 2, and so on.

"Details are found in Swift documentation online here."

A helpful addition to the standard set of datatypes from JavaScript is the 'enum'. Like languages like C#, an enum is a way of giving more friendly names to sets of numeric values.

enum Cardsuit {Clubs, Diamonds, Hearts, Spades};
var c: Cardsuit = Cardsuit.Diamonds;

By default, enums begin numbering their members starting at 0. This can be changed by manually setting the value of one its members. For example, the prior example can start at 1 instead of 0:

enum Cardsuit {Clubs = 1, Diamonds, Hearts, Spades};
var c: Cardsuit = Cardsuit.Diamonds;

Or, even manually set all the values in the enum:

enum Cardsuit {Clubs = 1, Diamonds = 2, Hearts = 4, Spades = 8};
var c: Cardsuit = Cardsuit.Diamonds;

A handy feature of enums in TypeScript is that you can also go from a numeric value to the name of that value in the enum. For example, if presented with the value 2 but unsure which that mapped to in the enum, one could look up the corresponding name:

enum Cardsuit {Clubs = 1, Diamonds, Hearts, Spades};
var suitName: string = Cardsuit[2];

alert(suitName);

An enum module was added to the Python standard library in version 3.4.

from enum import Enum
class Cards(Enum):
    clubs = 1
    diamonds = 2
    hearts = 3
    spades = 4

There is also a functional API for creating enumerations with automatically generated indices (starting with one):

Cards = Enum("Cards", ["clubs", "diamonds", "hearts", "spades"])

Python enumerations do not enforce semantic correctness (a meaningless comparison to an incompatible enumeration always returns False rather than raising a TypeError):

>>> Color = Enum("Color", ["red", "green", "blue"])
>>> Shape = Enum("Shape", ["circle", "triangle", "square", "hexagon"])
>>> def has_vertices(shape):
... 	return shape != Shape.circle
...
>>> has_vertices(Color.green)
True

Fortran only has enumerated types for interoperability with C; hence, the semantics is similar to C and, as in C, the enum values are just integers and no further type check is done. The C example from above can be written in Fortran as

  enum, bind( C )
    enumerator :: CLUBS = 1, DIAMONDS = 2, HEARTS = 4, SPADES = 8
  end enum

Enumerated datatypes in Visual Basic (up to version 6) and VBA are automatically assigned the "Long" datatype and also become a datatype themselves:

'Zero-based
Enum CardSuit
  Clubs
  Diamonds
  Hearts
  Spades
End Enum

Sub EnumExample()
  Dim suit As CardSuit
  suit = Diamonds
  MsgBox suit
End Sub

Example Code in VB.NET

Enum CardSuit
  Clubs
  Diamonds
  Hearts
  Spades
End Enum

Sub EnumExample()
  Dim suit As CardSuit
  suit = CardSuit.Diamonds
  MessageBox.show(suit)
End Sub

Common Lisp uses the member type specifier, e.g.,

(deftype cardsuit ()
  '(member club diamond heart spade))

that states that object is of type cardsuit if it is #'eql to club, diamond, heart or spade. The member type specifier is not valid as a Common Lisp Object System (CLOS) parameter specializer, however. Instead, (eql atom), which is the equivalent to (member atom) may be used (that is, only one member of the set may be specified with an eql type specifier, however, it may be used as a CLOS parameter specializer.) In other words, to define methods to cover an enumerated type, a method must be defined for each specific element of that type.

Additionally,

(deftype finite-element-set-type (&rest elements)
   `(member ,@elements))

may be used to define arbitrary enumerated types at runtime. For instance

(finite-element-set-type club diamond heart spade)

would refer to a type equivalent to the prior definition of cardsuit, as of course would simply have been using

(member club diamond heart spade)

but may be less confusing with the function #'member for stylistic reasons.