在C ++ 17中解压缩可变参数元组 [英] Unpacking variadic tuples in c++17

问题描述

在c ++ 17(也许是C ++ 2a)中，有什么比用

Is there anything better in c++17 (maybe C++2a) than the classic C++14 way to unpack variadic tuple with std::index_sequence?

有什么比这更好的了:

template <typename ...I>
class MultiIterator
{
public:
    MultiIterator(I const& ...i)
        : i(i...)
    {}

    MultiIterator& operator ++()
    {
        increment(std::index_sequence_for<I...>{});
        return *this;
    }


private:
    template <std::size_t ...C>
    void increment(std::index_sequence<C...>)
    {
        std::ignore = std::make_tuple(++std::get<C>(i)...);
    }

    std::tuple<I...> i;
};

类似于折叠表达式，

Like fold expression, structured-bindings? Any hint? I can accept answer why I cannot use these mentioned C++17 features here - but I prefer "solution.

推荐答案

自C ++ 14起，我们具有通用的lambda，而自C ++ 17起，我们具有有效的折叠表达式和 std :: apply 隐藏通常的拆包逻辑:

Since C++14 we have generic lambdas, and since C++17 we have fold expressions and std::apply effectively hiding the usual unpack logic:

std::apply( [](auto&... i){ ((void)++i,...); }, some_tuple );

---

注意:为您提供信息，(void)只是为了避免任何自定义逗号运算符插入...您永远不会知道:)

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