#include <cstdlib>
#include <iostream>
#include <set>
#include <string>
#include <iterator>

#include <tuple>

struct S {
    int n;
    std::string s;
    float d;
    bool operator<(const S& rhs) const
    {
        // compares n to rhs.n,
        // then s to rhs.s,
        // then d to rhs.d
        return std::tie(n, s, d) < std::tie(rhs.n, rhs.s, rhs.d);
    }
};

int main()
{
    std::set<S> mySet;

    // pre C++17:
    {
	    S value{42, "Test", 3.14};
	    std::set<S>::iterator iter;
	    bool inserted;

	    // unpacks the return val of insert into iter and inserted
	    std::tie(iter, inserted) = mySet.insert(value);

	    if (inserted)
		    std::cout << "Value was inserted\n";
    }

	// with C++17:
    {
        S value{100, "abc", 100.0};
        const auto [iter, inserted] = mySet.insert(value);

        if (inserted)
		    std::cout << "Value(" << iter->n << ", " << iter->s << ", ...) was inserted" << "\n";
    }
}