Editing Design by contract (section)

{{Short description|Approach for designing software}}
[[File:Design by contract.svg|thumbnail|A design by contract scheme]]
'''Design by contract''' ('''DbC'''), also known as '''contract programming''', '''programming by contract''' and '''design-by-contract programming''', is an approach for [[software design|designing software]].

It prescribes that software designers should define [[Formal methods|formal]], precise and verifiable interface specifications for [[Component-based software engineering#Software component|software components]], which extend the ordinary definition of [[abstract data type]]s with [[precondition]]s, [[postcondition]]s and [[Invariant (computer science)|invariants]]. These specifications are referred to as "contracts", in accordance with a [[conceptual metaphor]] with the conditions and obligations of business contracts.

The DbC approach [[Offensive_programming|assumes]] all ''client components'' that invoke an operation on a ''server component'' will meet the preconditions specified as required for that operation.

Where this assumption is considered too risky (as in multi-channel or [[distributed computing]]), the [[defensive_programming|inverse approach]] is taken, meaning that the ''server component'' tests that all relevant preconditions hold true (before, or while, processing the ''client component'''s request) and replies with a suitable error message if not.