c++ - 使用类型 T 的 std::array 构造类型可从 T 构造的 std::array

Question

请考虑这些类型:

struct Part
{
    float data;
};

struct Wrap
{
    Wrap( const Part& p )
        :data( p.data )
    {}
    float data;
};

现在我想使用 std::array<Part, N>初始化 std::array<Wrap, N> .

int main()
{
    std::array<Part, 3> parts{ Part{ 1.0f }, Part{ 2.0f }, Part{ 3.0f } };
    std::array<Wrap, 3> wrappers( parts );
    return 0;
}

(这会引发错误 "conversion from 'std::array<Part, 3>' to non-scalar type 'std::array<Wrap, 3>' requested")

如何使用 std::array类型 T初始化 std::array可从 T 构建的类型？

Answer 1

您可以使用辅助函数来自动转换:

// Convert each element based on a sequence of indices:
template<typename ToType, typename FromType, std::size_t... Indices>
std::array<ToType, sizeof...(Indices)>
convert_impl(const std::array<FromType, sizeof...(Indices)>& input, std::index_sequence<Indices...>)
{
    return {ToType(std::get<Indices>(input))...};
}

// Wraps convert_impl to hide the use of index_sequence from users:
template<typename ToType, typename FromType, std::size_t N>
std::array<ToType, N> convert(const std::array<FromType, N>& input)
{
    return convert_impl<ToType>(input, std::make_index_sequence<N>{});
}

int main()
{
    std::array<Part, 3> parts {Part{1.0f}, Part{2.0f}, Part{3.0f}};
    std::array<Wrap, 3> wraps = convert<Wrap>(parts);

    return 0;
}