unmodifiable

Unmodifiable describes objects or data structures whose exposed interface does not permit altering their state through that interface. In software design, an unmodifiable collection is one that cannot be changed via its public methods, ensuring read-only access for clients.

Unmodifiable is often implemented as a wrapper or view around a modifiable underlying object. These wrappers allow reading data but block mutating operations, either by throwing exceptions or by ignoring mutating calls. This concept differs from immutability: immutability means the value cannot change after creation, regardless of any references. An unmodifiable view, by contrast, may reflect changes made to the underlying data by other code.

Common contexts include collections and maps in programming languages. For example, a language or library may provide an unmodifiable wrapper around a list, map, or set, enabling safe read-only access while preserving the ability for the original data to change elsewhere. In some ecosystems, immutable data structures are preferred to guarantee that no changes can occur, whereas unmodifiable views provide protection against accidental modification without requiring full immutability.

Use cases and implications. Unmodifiable interfaces support encapsulation, safer APIs, and clearer contracts by signaling that consumers should not attempt to mutate the object. They can aid thread-safety by limiting mutation from certain paths. However, they do not inherently protect against concurrent modifications to the underlying data, nor do they guarantee immutability if references to the original object exist outside the unmodifiable view. Understanding the distinction between unmodifiable and immutable helps in designing robust data access patterns.