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// Author: Huahua #include <iostream> #include <string> #include <vector> #include <list> #include <tuple> using namespace std; // Python-Like enumerate() In C++17 // http://reedbeta.com/blog/python-like-enumerate-in-cpp17/ template <typename T, typename TIter = decltype(std::begin(std::declval<T>())), typename = decltype(std::end(std::declval<T>()))> constexpr auto enumerate(T && iterable) { struct iterator { int i; TIter iter; bool operator != (const iterator & other) const { return iter != other.iter; } void operator ++ () { ++i; ++iter; } auto operator * () const { return std::tie(i, *iter); } }; struct iterable_wrapper { T iterable; auto begin() { return iterator{ 0, std::begin(iterable) }; } auto end() { return iterator{ 0, std::end(iterable) }; } }; // return iterable_wrapper{ iterable }; // this makes a copy if iterable is a rvalue. return iterable_wrapper{ std::forward<T>(iterable) }; } struct A { int val; A(int val): val(val) { cout << "A(int)" << endl; } A(const A& a): val(a.val) { cout << "A(A&)" << endl; } A(A&& a): val(a.val) { cout << "A(A&&)" << endl; } }; int main(int argc, char** argv) { vector<int> arr{1, 2, 4}; for (size_t i = 0; i < arr.size(); ++i) cout << i << " " << arr[i] << endl; size_t idx = 0; for (int v : arr) cout << idx++ << " " << v << endl; for (auto it = begin(arr); it != end(arr); ++it) cout << distance(begin(arr), it) << " " << *it << endl; for (const auto& [i, v] : enumerate(arr)) cout << i << " " << v << endl; list<string> lst{"hello", "world!"}; for (const auto& [i, v] : enumerate(lst)) cout << i << " " << v << endl; for (const auto& [i, v] : enumerate(string("abcde"))) cout << i << " " << v << endl; vector<A> vec; vec.reserve(3); vec.emplace_back(1); vec.emplace_back(2); vec.emplace_back(4); for (const auto& [i, v] : enumerate(vec)) cout << i << " " << v.val << endl; for (const auto& [i, v] : enumerate(vector<A>{A(1), A(2), A(4)})) cout << i << " " << v.val << endl; return 0; } |