Twoitem

Twoitem is a term used in software design to denote a container that holds exactly two elements. It is effectively a programming analogue of the mathematical concept of a pair or a 2-tuple. In practice, twoitem may be implemented as a dedicated data type or as a generic construct that stores two values of possibly different types. The key characteristics are fixed size, and the two components are typically referred to as the first and second elements.

In languages with built-in support for pairs or tuples, twoitem is realized directly as a pair or a two-tuple. For example, Python exposes two-element tuples as (a, b) and supports unpacking. Java lacks a standard pair type; libraries define Pair<A,B> or use AbstractMap.SimpleEntry. C# provides System.Tuple<T1,T2> and ValueTuple<T1,T2>. C++ offers std::pair<T1,T2>; Haskell uses (a,b). JavaScript commonly uses an array of length two [a, b] or a small pair utility. Across languages, twoitem is often treated as either immutable or optionally mutable, and as a structure whose elements can be of different types.

Semantics typically include equality and hashing based on both components, and destructuring or pattern matching to access the first and second elements. Limitations include fixed arity, potential naming inconsistency (pair, tuple, twoitem, 2-tuple), and a tendency to be less flexible than broader collection types.

Use cases include returning two results from a function, representing simple key-value pairs, or modeling coordinate pairs. See also: pair, tuple, 2-tuple, ordered pair, two-element container.