OrElselike

orElselike is a conceptual programming operator described as a shorthand for selecting a primary value when it exists, or a fallback value when it does not. The term is used in discussions about language ergonomics and in documentation that explores patterns for handling optional or missing data. It is not a standard keyword in any single language, but it resembles familiar mechanisms such as optional-or-default patterns and null-coalescing constructs.

Semantics and variants

OrElselike is typically defined with two operands: a value and a fallback. In its basic form, it returns the primary value if it is defined (non-null or non-undefined, depending on the language), otherwise it yields the fallback. There are two common variants:

- Eager: the fallback is evaluated or produced regardless of whether it is needed, which can incur unnecessary computation.

- Lazy: the fallback is provided as a thunk, function, or supplier that is invoked only if the primary value is missing, allowing for costly defaults to be avoided.

Relationship to existing constructs

OrElselike maps closely to several established patterns:

- Nullish coalescing operators (for example, ?? in JavaScript and C#) that select a defined value when the left-hand side is null or undefined.

- Elvis or ternary-style operators in various languages that select between a value and a default.

- Optional types with orElse-like methods in languages such as Java, where a fallback is supplied if the optional is empty.

Usage considerations

When designing orElselike usage, considerations include type compatibility between the primary value and the fallback, the cost of computing the fallback, and readability. In languages with side effects in fallbacks, lazy evaluation is often preferable to avoid unnecessary work.

Examples (pseudo-code)

orElselike(value, defaultValue)

orElselike(value, () => computeDefault())

See also

orElse, nullish coalescing operator, Elvis operator, Optional, fallback pattern.