interiormutable

Interiormutable is a term used in some programming contexts, particularly in languages that distinguish between mutable and immutable data structures. It refers to an object or data structure whose internal state can be modified after its creation, but whose external representation or interface remains constant. This concept is often contrasted with truly mutable objects where both internal state and external behavior can change.

The idea behind interiormutable objects is to offer a compromise between the safety of immutability and the flexibility of mutability. While the underlying data might be altered for efficiency or internal bookkeeping, the ways in which other parts of the program can interact with the object are effectively fixed. This can provide some of the benefits of immutability, such as simpler reasoning about program state and potential for optimizations, without sacrificing the ability to perform internal updates.

An example might be a cache that internally reorders its elements or replaces them with updated versions, but always presents the same set of keys and associated values to the outside world. The interface it exposes – say, methods for `get` or `contains` – does not change, even though the internal mechanisms for fulfilling those requests might be modified. This distinction helps maintain a predictable contract for users of the interiormutable object.