enums

An enumeration, or enum, is a data type that defines a finite set of named values. Each value is a distinct member of the domain and can be treated as a value of the type. Enums model discrete categories, such as days of the week, cardinal directions, or status codes, and they help improve code readability and enforce that variables stay within a defined set.

Semantics vary among languages. In many imperative languages, an enum has an underlying integral type and the first enumerator defaults to zero, with subsequent ones incremented by one, unless explicitly assigned. Some languages, like C# and Rust, support custom underlying types or strongly typed enums that do not implicitly convert to numbers. Other languages provide string-based enums where the variants map to string values rather than numbers.

Common features include: underlying type selection, scope of names, explicit versus automatic value assignment, and the ability to perform comparisons against the defined set. Flags-style enums reuse powers of two so values can be combined with bitwise operators to represent multiple options, a pattern common in C and C#.

Enumeration values can often be enumerated, converted to and from their numeric or string representations, and used in control structures such as switch or match statements. Limitations include portability of underlying representations and varying support for iteration or reflection.

Examples:

C: enum Color { Red, Green, Blue };

C#: enum Color { Red = 0, Green = 1, Blue = 2 };

TypeScript: enum Color { Red, Green, Blue }