您如何为标准库容器定义 C++ 概念？

Question

我想为标准库容器实现一个 C++ 概念。

提前非常感谢！

Answer 1

有Container 的前置概念要求。作为一个看起来像的概念

template <class T>
concept container = requires(T a, const T b)
{
    requires regular<T>;
    requires swappable<T>;
    requires erasable<typename T::value_type>;
    requires same<typename T::reference, typename T::value_type &>;
    requires same<typename T::const_reference, const typename T::value_type &>;
    requires forward_iterator<typename T::iterator>;
    requires forward_iterator<typename T::const_iterator>;
    requires signed<typename T::difference_type>;
    requires same<typename T::difference_type, typename std::iterator_traits<typename T::iterator>::difference_type>;
    requires same<typename T::difference_type, typename std::iterator_traits<typename T::const_iterator>::difference_type>;
    { a.begin() } -> typename T::iterator;
    { a.end() } -> typename T::iterator;
    { b.begin() } -> typename T::const_iterator;
    { b.end() } -> typename T::const_iterator;
    { a.cbegin() } -> typename T::const_iterator;
    { a.cend() } -> typename T::const_iterator;
    { a.size() } -> typename T::size_type;
    { a.max_size() } -> typename T::size_type;
    { a.empty() } -> boolean;
};

虽然您想将其中的一些表达为requires range<T>

Answer 2

用 C++ 概念库修正了 Caleth 的答案：

    template <class ContainerType> 
    concept Container = requires(ContainerType a, const ContainerType b) 
    {
        requires std::regular<ContainerType>;
        requires std::swappable<ContainerType>;
        requires std::destructible<typename ContainerType::value_type>;
        requires std::same_as<typename ContainerType::reference, typename ContainerType::value_type &>;
        requires std::same_as<typename ContainerType::const_reference, const typename ContainerType::value_type &>;
        requires std::forward_iterator<typename ContainerType::iterator>;
        requires std::forward_iterator<typename ContainerType::const_iterator>;
        requires std::signed_integral<typename ContainerType::difference_type>;
        requires std::same_as<typename ContainerType::difference_type, typename std::iterator_traits<typename
    _ContainerType_::iterator>::difference_type>;
        requires std::same_as<typename ContainerType::difference_type, typename std::iterator_traits<typename
    _ContainerType_::const_iterator>::difference_type>;
        { a.begin() } -> typename ContainerType::iterator;
        { a.end() } -> typename ContainerType::iterator;
        { b.begin() } -> typename ContainerType::const_iterator;
        { b.end() } -> typename ContainerType::const_iterator;
        { a.cbegin() } -> typename ContainerType::const_iterator;
        { a.cend() } -> typename ContainerType::const_iterator;
        { a.size() } -> typename ContainerType::size_type;
        { a.max_size() } -> typename ContainerType::size_type;
        { a.empty() } -> boolean;
    };

Answer 3

在 C++ 中实际编译的固定版本...：

template <class ContainerType>
concept Container = requires(ContainerType a, const ContainerType b)
{
    requires std::regular<ContainerType>;
    requires std::swappable<ContainerType>;
    requires std::destructible<typename ContainerType::value_type>;
    requires std::same_as<typename ContainerType::reference, typename ContainerType::value_type &>;
    requires std::same_as<typename ContainerType::const_reference, const typename ContainerType::value_type &>;
    requires std::forward_iterator<typename ContainerType::iterator>;
    requires std::forward_iterator<typename ContainerType::const_iterator>;
    requires std::signed_integral<typename ContainerType::difference_type>;
    requires std::same_as<typename ContainerType::difference_type, typename std::iterator_traits<typename ContainerType::iterator>::difference_type>;
    requires std::same_as<typename ContainerType::difference_type, typename std::iterator_traits<typename ContainerType::const_iterator>::difference_type>;
    { a.begin() } -> std::same_as<typename ContainerType::iterator>;
    { a.end() } -> std::same_as<typename ContainerType::iterator>;
    { b.begin() } -> std::same_as<typename ContainerType::const_iterator>;
    { b.end() } -> std::same_as<typename ContainerType::const_iterator>;
    { a.cbegin() } -> std::same_as<typename ContainerType::const_iterator>;
    { a.cend() } -> std::same_as<typename ContainerType::const_iterator>;
    { a.size() } -> std::same_as<typename ContainerType::size_type>;
    { a.max_size() } -> std::same_as<typename ContainerType::size_type>;
    { a.empty() } -> std::same_as<bool>;
};
static_assert(Container<std::vector<unsigned char>>);
static_assert(Container<std::string>);