std::optional和std::expected是C++中两种重要的类型,用于处理可能不存在的值以及错误情况。std::optional侧重于值的存在性,而std::expected侧重于错误信息的传递和处理。在实际编程中,开发者需要根据具体的需求和场景来选择合适的类型。如果只是简单地处理值的有无,std::optional可能就足够了;如果需
C++23中std::optional和std::expected的单子式操作 一、引言在C++编程中,错误处理和可选值的管理是非常重要的部分。C++17引入了std::optional,它提供了一种新的标准方式来表达可能缺失的值。而C++23在此基础上,不仅对std::optional进行了扩展,还引入了std::expected,并且为它们都提供了受函数式编程启发的新接口,...
See the std::expected reference for more information. Using std::optional as an optional function parameter In lesson 12.11 -- Pass by address (part 2), we discussed how pass by address can be used to allow a function to accept an “optional” argument (that is, the caller can either ...
std::expected<T, E> 。由于 T 和 E 是不相交的类型,因此您知道从函数中返回了其中的哪一个。 这是您的函数,适用于您的 API 似乎具有的错误类型: namespace my_api { using error_t = int; enum : error_t { success = 0, invalid_input = 1, /* etc. */ }; } // namespace my_api ...
可是通常这些魔幻值需要接口使用者遵守函数的约定,为接口的使用增加了复杂度,基于此C++17提出了std::optional,用于解决值可能存在也可能不存在的问题。 std::optional<T>作为一个模板类,用于管理一个可选的容纳值(此处与std::tuple还是有区别的,tuple可以容纳n个值,获取函数执行结果的n种方式),容纳值可以是自定义...
static_assert(std::is_move_constructible<std::optional<NonMoveable>>::value); static_assert(std::is_move_assignable<std::optional<NonMoveable>>::value); int main(int argc, char* argv[]) { NonMoveable a1; NonMoveable a2{std::move(a1)}; // Bad, as expected std::optional<NonMoveable>...
expected (C++23) a wrapper that contains either an expected or error value (class template) ranges::single_viewviews::single (C++20) aviewthat contains a single element of a specified value (class template)(customization point object)
From cppreference.com Defined in header<optional> template<classT> classoptional; (since C++17) The class templatestd::optionalmanages an optional contained value, i.e. a value that may or may not be present. A common use case foroptionalis the return value of a function that may fail. ...
Expected / probable. Furthermore, we can see the error handling in terms of performance. We’d like it to be fast and using some additional machinery to facilitate errors might not be an option (like in the embedded world). Thus, for example, exceptions are considered “heavy” and usually...
value() << '\n'; else std::cout << "value no longer set\n"; } Output: false value set to 43 value no longer setSee alsooperator boolhas_value checks whether the object contains an expected value (public member function of std::expected<T,E>) ...