What Is Contract in Programming
Contract design is not a substitute for regular testing strategies such as unit testing, integration testing, and system testing. Rather, it complements external testing with internal self-testing that can be enabled both for isolated testing and in production code during a testing phase. When subcontracting, the functions replaced (at the time of compilation) in all public branches of the family tree are carefully researched (i.e. not only the direct public relatives of the derived class, but also all their public grandparents, etc.). In the case of multiple inheritance, this search (at compile time) also extends largely to all public structures in the multiple inheritance forest (several public base classes are searched for their declaration order in the inheritance list of the derived class). As is often the case with C++ multiple inheritance, this search can result in multiple functions being overwritten and thus subcontracted from multiple public base classes. Note that only public base classes are considered for outsourcing, because private and protected base classes are not accessible to the user on the calling site where the substitution principle applies. Contracts should not be allowed to change the status of the program, as they are only responsible for verifying (not changing) the status of the program to verify its compliance with specifications. Therefore, contracts should only access objects, function arguments, function return values, old values, and all other program variables in the const context (via const&, const* const, const volatile, etc.).
This supports class invariants and old values, but not sub-attacks (contracts are specified in definitions instead of declarations, and assertions are not consistently correct). When using contracts, a supplier should not try to verify that the terms of the contract are being met – a practice known as offensive programming – the general idea is that the code should “hit hard”, with contract review being the safety net. It is a C# extension that supports contract programming languages. The manufacturer`s prerequisites are validated before running the member initialization list so that the programming of these initializations can be simplified, provided that the manufacturer`s prerequisites are met (for example. B, constructor arguments can be validated by the constructor`s prerequisites before being used to initialize base classes and data members). Code contract tools currently assume that the following code elements are pure: The contract for a class or interface in Java or another OO language typically refers to the publicly available methods (or functions) and properties (or fields or attributes) of that class interface, as well as any comments or documentation that apply to those public methods and properties. The Digital Mars C++ compiler extends C++ and adds support for contract programming languages (among many other features). Let`s start with the most popular library for Python contracts: pycontracts. It performs simple checks of your function arguments and defines a DSL for simple comparisons, such as .B. “This list contains at least three items.” These can be very useful, but they show two tropics that we see in many contract implementations: the use of contracts as type reviewers and the processing of contract syntax as independent of the programming language.
I believe that the former has played an important role in moving contracts away from the mainstream: contracts make very bad systems. You can dismiss it as “like a static type system, but worse” or as “I didn`t need guys anyway, why bother with contracts?” I mean, you can definitely do it: in general, this library can`t meet that requirement. But even if contracts are programmed with the body in the function definition, it is still quite easy for users to simply identify and read the contractual part of the function definition (since the contract code must always be programmed at the top of the function definition). See Separate body implementation for information on how to use this library to program contract specifications outside of the body implementation (but at the expense of writing an additional function for a particular function, so this is generally not recommended). If the method of a class provides some functionality in object-oriented programming, it can: Contracts are part of the program specification and not part of its implementation. Therefore, contracts should ideally be programmed in C++ declarations and not in definitions. When if-then-throw statements are displayed under this form, the tools recognize them as legacy query statements. If no other contract follows the if-then-throw sequence, complete the code using the Contract.EndContractBlock method. [a] Reasoning: The authors of [N1962] decided to exclude classes derived from subcontractors` preconditions because they found that such a feature was rarely, if ever, used (see Re: [boost] [contract] diff n1962). Nevertheless, it should be noted that even in [N1962], when a derived class replaces two functions with prerequisites from two different base classes via multiple inheritance, the preponderant function contract verifies the prerequisites of its two base class functions in OR (so that even in [N1962] the prerequisites can indirectly subcontract when multiple inheritance is used). In addition, the conditions of subcontracting are clearly defined by the principle of substitution, so that this library allows to subcontract prerequisites such as Eiffel (users can avoid using this feature at any time when they do not need it). .