如何使用数字索引转换 varadic std::tuple 的所有元素? [英] How do I transform all elements of a varadic std::tuple using numerical indices?

问题描述

目前，我有一个这样的实现，以便使用一个函数 bar() 来转换元组的所有值，该函数接受元组的每个元素.

Currently, I have an implementation like this in order to transform all values of a tuple using a function bar() that takes in each element of the tuple.

template<typename ... Args>
void foo(const std::tuple<Args...>& a)
{
    std::tuple<Args...> transformedTuple = std::make_tuple(bar(std::get<Args>(a))...);
}

这样做的问题是，如果 Args 包含重复类型，这将不再起作用.因此，我想更改 std::get<> 调用以在元组中使用数字索引而不是使用类型.鉴于我的开发环境停留在 C++14 上，有没有办法让它工作?谢谢！

The problem with this is that this will no longer work if Args contains duplicate types. Hence, I would like to change the std::get<> call to use numerical indices into the tuple instead of using types. Given that my development environment is stuck on C++14, is there any way of getting this to work? Thanks!

推荐答案

您可以使用带有 std::integer_sequence 来做到这一点.添加一个接受 integer_sequence 之类的辅助函数

You can use a helper function that takes a std::integer_sequence to do this. Add a helper function that takes an integer_sequence like

template<typename Tuple, std::size_t... I>
auto foo_helper(const Tuple& a, std::integer_sequence<std::size_t, I...>)
{
    return std::make_tuple(bar(std::get<I>(a))...);
}

然后改变 foo 来调用 helper 就像

And then changing foo to call the helper like

template<typename ... Args>
auto foo(const std::tuple<Args...>& a)
{
    return foo_helper(a, std::make_index_sequence<sizeof...(Args)>{});
}

现场演示

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