q_map.cpp

#include <iostream>
#include <vector>
#include <unordered_map>

using namespace std;

struct Lake {
    string name;
};

struct Distance{};
 
int main() {
    
    unordered_map<Lake, Distance> ls = {
        {Lake{"Near"},Distance()}, 
        {Lake{"Far"},Distance()}};  
   
    for (auto [k,_]: ls) {
        cout << k << '\n';
    }
        
}

https://coliru.stacked-crooked.com/a/9d4b378072bef35d