optionalordefault

optionalordefault is a term used in software design to describe a dual mechanism for handling missing values: a field or parameter may be optional, or it may carry a default value if omitted. It is not a formal keyword in mainstream languages, but appears in design guides and schema definitions as a way to express semantics clearly.

The concept distinguishes two states: absence and default. Optional indicates the value may be omitted entirely, leaving the value undefined or null; default indicates that a predefined value is substituted when the value is not provided. Some systems use a combined annotation or guidance called optionalordefault to indicate both possibilities, allowing an API or data model to support explicit omittance and automatic substitution without requiring separate flags.

In practice, implementing optionalordefault requires careful handling to avoid ambiguity between missing values and values set to null. Schemas might declare a field as optional with a default, and code may implement logic such as: if value is undefined, assign default; if value is null and null is allowed, treat as null; otherwise, use the provided value. Clear rules help prevent inconsistent behavior across clients and servers.

In API and data modeling contexts, optionalordefault can improve backward compatibility and clarity when evolving interfaces, particularly in versioned REST APIs and JSON payloads. It aligns with patterns that minimize breaking changes by letting clients omit fields while servers can supply sensible defaults.

See also: optional parameter, default value, JSON Schema, nullability, schema design.