getonly

Getonly refers to a property or data exposure pattern in software design that allows reading a value but not writing it from outside the defining scope. The get-only approach ensures that consumers can observe state but cannot alter it directly, preserving invariants and aiding thread safety.

Implementation patterns vary by language but share a common idea: expose a public getter while omitting a public setter, or provide a setter with restricted access. In C#, a get-only property can be declared so that external code cannot assign a new value. In Java, a private field is typically exposed through a public getter with no corresponding setter. In Python, a property can be defined with @property and no setter, making it effectively read-only from the outside. TypeScript and JavaScript support getters without setters, and many languages offer a separate concept of a read-only or immutable type for collections, such as IReadOnlyList or ReadonlyArray.

Applications and advantages include stronger encapsulation, clearer boundaries between internal state and external usage, and easier maintenance of invariants. Getonly patterns can simplify reasoning about state changes and can enable safe lazy initialization or caching strategies, since external code cannot directly mutate exposed data.

Limitations and caveats involve ensuring true immutability when the exposed value references mutable objects. Returning a mutable object may allow external code to modify internal state indirectly, so deep copies or immutable views are sometimes necessary. Overemphasis on get-only access can reduce API flexibility, so developers balance immutability with practical needs for mutation in controlled contexts.

See also: immutability, encapsulation, read-only, property accessors.