Abstract

We present a minimal system for expressing interface requirements as contracts. They provide basic mitigation measures for early containment of undesired program behavior. The set of facilities suggested in this proposal is deliberately kept to the minimum of pre-conditions and post-conditions. Contracts are part of an operation’s interface, but not part of its type. That is, while the expression of contracts is logically part of the operation’s interface, the actual code verifying the conditions are part of the operation’s implementation. 1 WHAT ARE CONTRACTS? Contracts are requirements that an operation puts on its arguments for successful completion and set of guarantees it provides upon successful completion. The former is known as pre-condition and the latter is called post-condition. Contracts are part of the interface of an operation as a programmer (consumer or producer) sees it, e.g. “What do I have to do to call this function? ” and “What may I rely on when implementing this function? ” However, contracts (as suggested in this proposal) are not part of the type system.