useor

Useor is a hypothetical binary operator discussed in programming language design and logic. It is intended to model a fallback choice between two expressions or resources, returning the first usable value. Unlike a standard logical OR, useor is defined with an emphasis on the notion of usability rather than truthiness alone.

Semantics vary across proposals, but common definitions include: (1) the left-most usable value wins; a value is usable if it is defined and not an error; (2) short-circuit: the second expression is not evaluated if the first is usable. In practice, useor can support resources such as a primary and a secondary. The typical form is: result = useor(primary(), secondary()). If primary() yields a defined value, that is returned; otherwise, secondary() is evaluated and returned.

Evaluation concerns accompany useor. Side effects in the first expression can complicate semantics, and languages with strict evaluation must specify that only the necessary expression is invoked. Lazy evaluation can reduce these risks by delaying evaluation of the second operand until needed. Uses of useor include error handling, fallback strategies, resource selection, and feature toggles in experimental language designs.

Limitations include its status as a non-standard, theoretical construct, potential confusion with existing operators, and possible performance costs if both expressions are expensive. Proponents argue it can simplify certain fallback patterns, while critics caution about clarity and portability across languages.

See also: or operator, null-coalescing operator, fallback, short-circuit evaluation, lazy evaluation.