类型安全 - all_of/ any_of/ none_of for std::tuple

type safety - all_of/ any_of/ none_of for std::tuple

本文关键字：of std tuple for none 类型安全 any all      更新时间：2023-10-16

所以我开始实现一些模仿STL算法行为的算法，但使用异构容器，又名std：：tuple。 

template<typename UnaryPredicate, typename Tuple>
bool all_of(UnaryPredicate&& p, Tuple&& t) noexcept
{
    return std::apply([&p](auto&& ...xs){ return (p(std::forward<decltype(xs)>(xs)) && ...); }, std::forward<Tuple>(t));
}
template<typename UnaryPredicate, typename Tuple>
bool any_of(UnaryPredicate&& p, Tuple&& t) noexcept
{
    return std::apply([&p](auto&& ...xs){ return (p(std::forward<decltype(xs)>(xs)) || ...); }, std::forward<Tuple>(t));
}
template<typename UnaryPredicate, typename Tuple>
bool none_of(UnaryPredicate&& p, Tuple&& t) noexcept
{
    return std::apply([&p](auto&& ...xs){ return !(p(std::forward<decltype(xs)>(xs)) || ...); }, std::forward<Tuple>(t));
}

如果您使用返回布尔值的一元谓词，所有这些工作正常。但是，如果没有呢？如何确保 UnaryPredicate 在使用元组的每个元素调用时返回布尔值？另外，我如何检查UnaryPredicate是否实际上没有引发任何异常。

我知道有像"is_nothrow_invocable"和"invoke_result"这样的类型特征，但所有这些都需要元组包含的元素类型。我真的必须使用"algorithm_impl"模式吗？

namespace impl
{
    template<typename UnaryPredicate, typename Tuple, auto ...Is>
    bool all_of_impl(UnaryPredicate&& p, Tuple&& t, std::index_sequence<Is...>) noexcept
    {
        return std::apply([&p](auto&& ...xs){ return (p(std::forward<decltype(xs)>(xs)) && ...); }, std::forward<Tuple>(t));
    }
}
template<typename UnaryPredicate, typename Tuple>
bool all_of(UnaryPredicate&& p, Tuple&& t) noexcept
{
    return impl::all_of_impl(std::forward<UnaryPredicate>(p), std::forward<Tuple>(t), std::make_index_sequence<std::tuple_size_v<std::decay_t<Tuple>>>{});
}

现在我可以做这样的事情：

std::enable_if_t<std::conjunction_v<std::is_same<std::invoke_result_t<std::decay_t<UnaryPredicate>, std::tuple_element_t<Is, std::decay_t<Tuple>>>, bool>...>, bool>

但这真的是要走的路吗？

编辑：

好吧，一如既往，我把事情搞得太复杂了。我想我找到了一个可以接受的解决方案：

template<typename UnaryPredicate, typename Tuple>
struct helper;
template<typename UnaryPredicate, typename Tuple>
struct helper2;
template<typename UnaryPredicate, typename ...Ts>
struct helper<UnaryPredicate, std::tuple<Ts...>>
    : std::bool_constant<std::conjunction_v<std::is_same<bool, std::invoke_result_t<std::decay_t<UnaryPredicate>, std::decay_t<Ts>>>...>>
{};
template<typename UnaryPredicate, typename ...Ts>
struct helper2<UnaryPredicate, std::tuple<Ts...>>
    : std::bool_constant<std::conjunction_v<std::is_nothrow_invocable<std::decay_t<UnaryPredicate>, std::decay_t<Ts>>...>>
{};
template<typename UnaryPredicate, typename Tuple>
inline constexpr auto helper_v{ helper<UnaryPredicate, Tuple>::value };
template<typename UnaryPredicate, typename Tuple>
inline constexpr auto helper2_v{ helper2<UnaryPredicate, Tuple>::value };

template<typename UnaryPredicate, typename Tuple>
std::enable_if_t<helper_v<UnaryPredicate, Tuple>, bool> all_of(UnaryPredicate&& p, Tuple&& t) noexcept(helper2_v<UnaryPredicate, Tuple>)
{
    return std::apply([&p](auto&& ...xs){ return (p(std::forward<decltype(xs)>(xs)) && ...); }, std::forward<Tuple>(t));
}
template<typename UnaryPredicate, typename Tuple>
std::enable_if_t<helper_v<UnaryPredicate, Tuple>, bool> any_of(UnaryPredicate&& p, Tuple&& t) noexcept(helper2_v<UnaryPredicate, Tuple>)
{
    return std::apply([&p](auto&& ...xs){ return (p(std::forward<decltype(xs)>(xs)) || ...); }, std::forward<Tuple>(t));
}
template<typename UnaryPredicate, typename Tuple>
std::enable_if_t<helper_v<UnaryPredicate, Tuple>, bool> none_of(UnaryPredicate&& p, Tuple&& t) noexcept(helper2_v<UnaryPredicate, Tuple>)
{
    return std::apply([&p](auto&& ...xs){ return !(p(std::forward<decltype(xs)>(xs)) || ...); }, std::forward<Tuple>(t));
}

#define RETURNS(...) 
  noexcept(noexcept(__VA_ARGS__)) 
  -> decltype(__VA_ARGS__) 
  { return __VA_ARGS__; }
template<class UnaryPredicate, class Tuple>
auto all_of(UnaryPredicate&& p, Tuple&& t)
RETURNS(
  std::apply(
    [&p](auto&& ...xs){
      return (p(std::forward<decltype(xs)>(xs)) && ...);
    },
    std::forward<Tuple>(t)
  )
)

等

我找到了一个比我之前的编辑:)更好的解决方案

#include <functional>
#include <iostream>
#include <tuple>
#include <type_traits>
#include <utility>
template<typename UnaryFunction, typename ...Types>
constexpr std::enable_if_t<std::conjunction_v<std::is_same<std::invoke_result_t<UnaryFunction, Types>, bool>...>, bool> AllOf(UnaryFunction&& p, std::tuple<Types...>&& t) noexcept(std::conjunction_v<std::is_nothrow_invocable<UnaryFunction, Types>...>)
{
    return std::apply([&](auto&& ...xs) constexpr { return (p(std::forward<decltype(xs)>(xs)) && ...); }, std::forward<std::tuple<Types...>>(t));
}
template<typename UnaryFunction, typename ...Types>
constexpr std::enable_if_t<std::conjunction_v<std::is_same<std::invoke_result_t<UnaryFunction, Types>, bool>...>, bool> AnyOf(UnaryFunction&& p, std::tuple<Types...>&& t) noexcept(std::conjunction_v<std::is_nothrow_invocable<UnaryFunction, Types>...>)
{
    return std::apply([&](auto&& ...xs) constexpr { return (p(std::forward<decltype(xs)>(xs)) || ...); }, std::forward<std::tuple<Types...>>(t));
}
template<typename UnaryFunction, typename ...Types>
constexpr std::enable_if_t<std::conjunction_v<std::is_same<std::invoke_result_t<UnaryFunction, Types>, bool>...>, bool> NoneOf(UnaryFunction&& p, std::tuple<Types...>&& t) noexcept(std::conjunction_v<std::is_nothrow_invocable<UnaryFunction, Types>...>)
{
    return std::apply([&](auto&& ...xs) constexpr { return !(p(std::forward<decltype(xs)>(xs)) || ...); }, std::forward<std::tuple<Types...>>(t));
}
int main()
{  
    std::cout 
        << std::boolalpha 
        << AllOf([](auto&& x){ return x; }, std::make_tuple(true, true, true)) << "n"
        << AnyOf([](auto&& x){ return x; }, std::make_tuple(false, false, true)) << "n"
        << NoneOf([](auto&& x){ return x; }, std::make_tuple(false, false, false)) << "n";
}
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