Talk:BackwardCompatibility

From APIDesign

Regarding BackwardCompatibility and, in particular, Functional Compatibility, you suggest that the output must be "the same result", which implies that only deterministic functions can achieve functional compatibility.

It seems to me that Functional Compatibility would be met with much looser restrictions: that the output must not further restrict any pre-conditions, and must continue to meet all post-conditions, specified for the function. I.e the "same" result isn't required, but a result that remains within functional specifications is required. This is especially useful when describing updates to, say, constraint programming paradigms and situations where non-determinism is involved or allowed.

Achieving the same result should be another level above functional compatibility. Or perhaps the above could be a lower level, like 'interface' compatibility. But coupling at the level of 'functional compatibility' would then be a clearer no-no: it means the project is coupled to the implementation rather than the interface.