fill-no-initializer-list.cpp

#include <unordered_map>
#include <utility>
#include <iostream>

using namespace std;

template<class T1, class T2> void fill(unordered_map<T1, T2>& m) {}

template<class T1, class T2, class Key, class Value, class... Args>
void fill(unordered_map<T1, T2>& m, Key&& key, Value&& value, Args&&... args) {
    m.insert({ forward<Key>(key), forward<Value>(value) });
    fill(m, forward<Args>(args)...);
}

template<class T1, class T2, class... Args>
unordered_map<T1, T2> unordered_map_init(Args&&... args) {
    auto m = unordered_map<T1, T2>{};

    fill(m, forward<Args>(args)...);

    return m;
}

int main() {
    static auto m = unordered_map_init<int, int>(1, 2, 3, 4);

    for (auto& p : m) cout << p.first << " => " << p.second << endl;
}