Modernes C++ programmieren

// https://godbolt.org/z/jGfeT94as 
#include <string>
#include <set>
#include <iostream>
#include <tuple> // tuple, tie
using std::string; using std::set; using std::cout; using std::tie;
struct Hobbit {
  string vorname;
  string nachname;
  Hobbit(const string v, const string n) : vorname{v}, nachname{n} {}
};
struct CompNachname {
  bool operator()(const Hobbit& x, const Hobbit& y) const { // normales <
    return tie(x.nachname, x.vorname) < tie(y.nachname, y.vorname);
  }
  using is_transparent = std::true_type; // für find erlaubt
  bool operator()(const Hobbit& x, const string& y) const { // für find etc.
    return x.nachname < y;
  }
  bool operator()(const string& x, const Hobbit& y) const { // für find etc.
    return x < y.nachname;
  }
};
int main() {
    using namespace std::literals; // erlaube "…"s
    set<Hobbit,CompNachname> hobbits;
    hobbits.emplace( "Frodo", "Baggins" );
    hobbits.emplace( "Sam", "Gamgee" );
    auto f1 = hobbits.find( Hobbit{"Frodo", "Baggins"} ); // ganzer Schlüssel
    if(f1 != hobbits.end()) {
        cout << "gefunden: " << f1->vorname << '\n'; // Frodo
    }
    auto f2 = hobbits.find( "Gamgee"s );             // äquivalenter Schlüssel
    if(f2 != hobbits.end()) {
        cout << "gefunden: " << f2->vorname << '\n'; // Sam
    }
}