Information hiding

Information hiding is a design principle coined by David Parnas. It states that a component should shield its callers from its internal decisions. It is often described as "hiding implementation details".

Information hiding is synonymous with abstraction, and encapsulation is the practical implementation of it — though all three terms are used interchangeably. The design pattern is that a component exposes an interface and conceals everything behind that interface. Callers depend only on what the interface promises and not on the component’s internal elements.

With proper encapsulation, in which the internal implementation details are not merely hidden, but fully isolated, from the outside world, components behave like black boxes.

The fundamental principle of information hiding is to encapsulate what changes, which means to hide behind an interface any potentially volatile implementation details — anything that is likely to change in the future. This protects other parts of a system from modification if the implementation of any single component is re-evaluated.

Information hiding is a derivative of the approach of incremental refinement along the control flow. One of the trade-offs of information hiding is that it can make it harder to work bottom-up.

Components are said to have leaky abstractions when implementation details are exposed through their interface, making the implementation resistent to change because of the wider refactoring that would be required beyond the component.