问题
I would like to know how to access the n-th value of an std::integer_sequence. For example given a type
using foo = std::integer_sequence<int, 3, 1, 4>;
I would like to have something like
auto i = get<foo, 2>(); // i = 4
Is there something in the standard library to do that? If not, do I need to resort to an iterative solution if I want this to work in C++14 (not C++17) ?
回答1:
There is no such built-in method as far as I'm aware but you can implement it itself in a few neat lines without any iterations:
template<class T, T... Ints>
constexpr T get(std::integer_sequence<T, Ints...>, std::size_t i) {
constexpr T arr[] = {Ints...};
return arr[i];
}
See how it works here: https://godbolt.org/z/yAfMeg
Arguments can be lifted into template parameters (to match your example) with a bit more code.
来源：https://stackoverflow.com/questions/53223910/how-to-access-n-th-value-of-an-integer-sequence