dom/canvas/TupleUtils.h

   1 /* This Source Code Form is subject to the terms of the Mozilla Public
   2  * License, v. 2.0. If a copy of the MPL was not distributed with this
   3  * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
   4
   5 #ifndef DOM_CANVAS_TUPLE_UTILS_H
   6 #define DOM_CANVAS_TUPLE_UTILS_H
   7
   8 #include <tuple>
   9
  10 namespace mozilla {
  11
  12 // -
  13 // ToTupleOfConstRefs
  14
  15 template <class T>
  16 constexpr const auto& ToConstRef1(T& ret) {
  17   return ret;
  18 }
  19
  20 template <class Tup, size_t... Ids>
  21 constexpr auto ToTupleOfConstRefsN(const Tup& tup,
  22                                    const std::index_sequence<Ids...>&) {
  23   return std::tie(ToConstRef1(std::get<Ids>(tup))...);
  24 }
  25
  26 template <class... Args, size_t... Ids, class Tup = std::tuple<Args...>>
  27 constexpr auto ToTupleOfConstRefs(const Tup& tup) {
  28   return ToTupleOfConstRefsN(
  29       tup, std::make_index_sequence<std::tuple_size_v<Tup>>());
  30 }
  31
  32 // -
  33 // MapTuple
  34
  35 template <class Tup, class Callable, size_t... Ids>
  36 constexpr auto MapTupleN(Tup&& tup, Callable&& fn,
  37                          const std::index_sequence<Ids...>&) {
  38   return std::make_tuple(fn(std::get<Ids>(tup))...);
  39 }
  40
  41 /// Callable::operator()(T) cannot return void or you will get weird errors.
  42 template <class... Args, class Callable, class Tup = std::tuple<Args...>>
  43 constexpr auto MapTuple(Tup&& t, Callable&& fn) {
  44   using Tup2 = typename std::remove_reference<Tup>::type;
  45   return MapTupleN(t, fn, std::make_index_sequence<std::tuple_size_v<Tup2>>());
  46 }
  47
  48 // -
  49
  50 template <class Tup>
  51 struct SizeofTupleArgs;
  52
  53 // c++17 fold expressions make this easy, once we pull out the Args parameter
  54 // pack by constraining the default template:
  55 template <class... Args>
  56 struct SizeofTupleArgs<std::tuple<Args...>>
  57     : std::integral_constant<size_t, (... + sizeof(Args))> {};
  58
  59 static_assert(SizeofTupleArgs<std::tuple<size_t, char, char, char>>::value ==
  60               sizeof(size_t) + 3);
  61
  62 }  // namespace mozilla
  63
  64 #endif  // DOM_CANVAS_TUPLE_UTILS_H