lst-0006-book.cpp
// https://godbolt.org/z/9qhMo6zbb
#include <iostream>
#include <string>
#include <tuple>
#include <map>
#include <unordered_set>
using std::tuple; using std::get; using std::cout; using std::string;
int main() {
std::map<tuple<int,string>,double> m { {{12,"x"},3.14} };
cout << m[{12,"x"}] << "\n"; // Output: 3.14
std::unordered_set<tuple<int,string>> s { {12,"x"} }; // (ERR) no std::hash
}