std::tie

#include <cassert>
#include <iostream>
#include <set>
#include <string>
#include <tuple>
 
struct S
{
 int n;
 std::string s;
 float d;
 
 friend bool operator<(const S& lhs, const S& rhs) noexcept
 {
 // compares lhs.n to rhs.n,
 // then lhs.s to rhs.s,
 // then lhs.d to rhs.d
 // in that order, first non-equal result is returned
 // or false if all elements are equal
 return std::tie(lhs.n, lhs.s, lhs.d) < std::tie(rhs.n, rhs.s, rhs.d);
 }
};
 
int main()
{
 // Lexicographical comparison demo:
 std::set <S> set_of_s;
 
 S value{42, "Test", 3.14};
 std::set <S>::iterator iter;
 bool is_inserted;
 
 // Unpack a pair:
 std::tie(iter, is_inserted) = set_of_s.insert(value);
 assert (is_inserted);
 
 
 // std::tie and structured bindings:
 auto position = [](int w) { return std::tuple (1 * w, 2 * w); };
 
 auto [x, y] = position(1);
 assert (x == 1 && y == 2);
 std::tie(x, y) = position(2); // reuse x, y with tie
 assert (x == 2 && y == 4);
 
 
 // Implicit conversions are permitted:
 std::tuple <char, short> coordinates(6, 9);
 std::tie(x, y) = coordinates;
 assert (x == 6 && y == 9);
 
 // Skip an element:
 std::string z;
 std::tie(x, std::ignore, z) = std::tuple (1, 2.0, "Test");
 assert (x == 1 && z == "Test");
}