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In this paper, we propose a Contracts facility for C++ that has been carefully considered by SG21 with a high bar set for level of consensus. The proposal includes syntax for specifying three kinds of contract assertions: precondition assertions, postcondition assertions, and assertion statements. In addition, we specify four evaluation semantics for these assertions — one non- checking semantic, ignore, and three checking semantics, observe, enforce, and quick_enforce — as well as the ability to specify a user-defined handler for contract violations. The features proposed in this paper allow C++ users to leverage contract assertions in their ecosystems in numerous ways.

Does the C++ design follow the zero-overhead principle? Should it? I think it should, even if that principle isn’t trivial to define precisely. Some of you (for some definition of “you”) seem not to. We– WG21 as an organization – haven’t taken it seriously enough to make it a requirement for acceptance of new features. I think that is a serious problem, but one that we (WG21) should be able to handle. This paper offers some examples.