pairtwo

Pairtwo is a term used in computer science and data modeling to denote a simple two-element pairing construct. In its most common form, pairtwo stores exactly two related values in a single composite object, often labeled as first and second. It is effectively a two-element tuple or 2-tuple and serves as a basic building block for representing associations, pairs of related records, or arguments to functions that operate on two inputs.

In programming languages that support product types, pairtwo can be implemented as a pair, a 2-tuple, or a small record. It is typically immutable in functional contexts, though mutable variants exist in imperative environments. Common operations include accessing the two components, applying a function to either component (mapFirst, mapSecond), and swapping the two elements. Pairtwo can also be serialized to formats such as JSON as a two-element array.

Usage patterns include serving as a lightweight container for related values, acting as a surrogate for key-value data when a dedicated map is unnecessary, or serving as a parameter pack for higher-order functions. Variants include labeled pairs (first, second) versus unlabeled pairs, as well as nested pairtwos to represent higher-arity data.

History and relationship to other concepts: the idea traces to the broader notion of product types and ordered pairs. In practice, many languages represent pairtwo as a language-native pair or two-element tuple, underscoring its role as a fundamental, low-overhead data carrier. See also: tuple, pair, product type, 2-tuple, zip.