Editing Abstraction (computer science) (section)

==Data abstraction==
{{Further|Abstract data type}}

Data abstraction enforces a clear separation between the ''abstract'' properties of a [[data type]] and the ''concrete'' details of its implementation. The abstract properties are those that are visible to client code that makes use of the data type—the ''interface'' to the data type—while the concrete implementation is kept entirely private, and indeed can change, for example to incorporate efficiency improvements over time. The idea is that such changes are not supposed to have any impact on client code, since they involve no difference in the abstract behaviour.

For example, one could define an [[abstract data type]] called ''lookup table'' which uniquely associates ''keys'' with ''values'', and in which values may be retrieved by specifying their corresponding keys. Such a lookup table may be implemented in various ways: as a [[hash table]], a [[binary search tree]], or even a simple linear [[List (computing)|list]] of (key:value) pairs. As far as client code is concerned, the abstract properties of the type are the same in each case.

Of course, this all relies on getting the details of the interface right in the first place, since any changes there can have major impacts on client code. As one way to look at this: the interface forms a ''contract'' on agreed behaviour between the data type and client code; anything not spelled out in the contract is subject to change without notice.