C++ python-like enumerate

enumerate.h

template<typename T> class enumerate {
	T& iteratable;
public:
	enumerate(T& iteratable) : iteratable(iteratable) {}
	template<typename I> class iterator {
		I it;
		int i = 0;
	public:
		iterator(I it) : it(it) {}
		iterator operator++() { let i = *this; operator++(0); return i; }
		iterator operator++(int) { it++; i++; return *this; }
		std::pair<const int, decltype(*it)&> operator*() { return {i, *it}; }
		bool operator==(const iterator& o) { return it == o.it; }
		bool operator!=(const iterator& o) { return !operator==(o); }
	};
	template<typename I> class const_iterator {
		I it;
		int i = 0;
	public:
		const_iterator(I it) : it(it) {}
		const_iterator operator++() { let i = *this; operator++(0); return i; }
		const_iterator operator++(int) { it++; i++; return *this; }
		std::pair<const int, const decltype(*it)&> operator*() const { return {i, *it}; }
		bool operator==(const const_iterator& o) const { return it == o.it; }
		bool operator!=(const const_iterator& o) const { return !operator==(o); }
	};
	decltype(auto) begin()       { return iterator(iteratable.begin());       }
	decltype(auto) end()         { return iterator(iteratable.end());         }
	decltype(auto) begin() const { return const_iterator(iteratable.begin()); }
	decltype(auto) end()   const { return const_iterator(iteratable.end());   }
};


// Example:
// std::vector<std::string> vec = {"hello", "there"};
// for(auto [i, str] : enumerate(vec)) {
//     ...
// }