orElseDefault

orElseDefault is a programming pattern used to obtain a value from an optional, nullable, or may-be container by supplying a fallback when no value is present. The goal is to avoid explicit null checks and to guarantee a concrete result in all code paths. In libraries that model optional presence, orElseDefault (or an equivalent operation) returns the contained value if it exists, otherwise it yields a default value.

There are two common forms of orElseDefault. The eager form uses a fixed default supplied as a value, such as orElseDefault(defaultValue). The lazy form accepts a supplier or function that computes the default only if needed, such as orElseDefault(() -> computeDefault()). The lazy variant can improve performance when computing the default is expensive or has side effects.

Usage and semantics. orElseDefault is typically used in pipelines or chains of operations where values may be missing, enabling concise handling of missing cases without explicit branching. It helps maintain functional-style readability and reduces boilerplate. However, care is needed regarding the nature of the default: it should be stable, deterministic, and free of unintended side effects, especially in lazy forms.

Relation to other concepts. The pattern aligns with similar constructs across languages, including getOrElse in Scala, unwrap_or_else in Rust, and the Elvis operator in Kotlin. While names vary, the core idea remains the same: provide a reliable value by supplying a fallback when a value is absent.

See also. Optional, Maybe/Option types, orElse, getOrElse, Elvis operator, unwrap_or_else.