OXYGENHUB
◆ main openmsx / src / utils / enumerate.hh
1.4 KiB · C++ · last changed chore(): initial commit 1 month ago source blame history raw
e8555c89 Andy McCall 1 
#ifndef ENUMERATE_HH
2 
#define ENUMERATE_HH
3
4 
/** Heavily inspired by Nathan Reed's blog post:
5 
  * Python-Like enumerate() In C++17
6 
  * http://reedbeta.com/blog/python-like-enumerate-in-cpp17/
7 
  *
8 
  * Can be used to simplify loops like:
9 
  *    for (size_t i = 0; i < std::size(my_array); ++i) {
10 
  *        auto& elem = my_array[i];
11 
  *        ... do stuff with 'i' and 'elem'
12 
  *    }
13 
  *
14 
  * With enumerate() that becomes:
15 
  *    for (auto [i, elem] : enumerate(my_array)) {
16 
  *        ... do stuff with 'i' and 'elem'
17 
  *    }
18 
  */
19
20 
#include <cstddef>
21 
#include <iterator>
22 
#include <tuple>
23 
#include <utility>
24
25 
template<typename Iterable,
26 
         typename Iter = decltype(std::begin(std::declval<Iterable>())),
27 
         typename      = decltype(std::end  (std::declval<Iterable>()))>
28 
constexpr auto enumerate(Iterable&& iterable)
29 
{
30 
	struct iterator {
31 
		size_t i;
32 
		Iter iter;
33
34 
		[[nodiscard]] constexpr bool operator==(const iterator& other) const {
35 
			return iter == other.iter;
36 
		}
37
38 
		[[nodiscard]] constexpr bool operator==(const Iter& other) const {
39 
			return iter == other;
40 
		}
41
42 
		constexpr void operator++() {
43 
			++i;
44 
			++iter;
45 
		}
46 
		constexpr auto operator*() const {
47 
			return std::tie(i, *iter);
48 
		}
49 
	};
50
51 
	struct iterable_wrapper {
52 
		Iterable iterable;
53
54 
		constexpr auto begin() {
55 
			return iterator{0, std::begin(iterable)};
56 
		}
57 
		constexpr auto end() {
58 
			return std::end(iterable);
59 
		}
60 
	};
61
62 
	return iterable_wrapper{std::forward<Iterable>(iterable)};
63 
}
64
65 
#endif