1 files changed, 64 insertions, 0 deletions
diff --git a/dom/canvas/TupleUtils.h b/dom/canvas/TupleUtils.h
new file mode 100644
index 0000000000..f5fe19378b
--- /dev/null
+++ b/dom/canvas/TupleUtils.h
@@ -0,0 +1,64 @@
+/* This Source Code Form is subject to the terms of the Mozilla Public
+ * License, v. 2.0. If a copy of the MPL was not distributed with this
+ * file, You can obtain one at http://mozilla.org/MPL/2.0/. */
+
+#ifndef DOM_CANVAS_TUPLE_UTILS_H
+#define DOM_CANVAS_TUPLE_UTILS_H
+
+#include <tuple>
+
+namespace mozilla {
+
+// -
+// ToTupleOfConstRefs
+
+template <class T>
+constexpr const auto& ToConstRef1(T& ret) {
+  return ret;
+}
+
+template <class Tup, size_t... Ids>
+constexpr auto ToTupleOfConstRefsN(const Tup& tup,
+                                   const std::index_sequence<Ids...>&) {
+  return std::tie(ToConstRef1(std::get<Ids>(tup))...);
+}
+
+template <class... Args, size_t... Ids, class Tup = std::tuple<Args...>>
+constexpr auto ToTupleOfConstRefs(const Tup& tup) {
+  return ToTupleOfConstRefsN(
+      tup, std::make_index_sequence<std::tuple_size_v<Tup>>());
+}
+
+// -
+// MapTuple
+
+template <class Tup, class Callable, size_t... Ids>
+constexpr auto MapTupleN(Tup&& tup, Callable&& fn,
+                         const std::index_sequence<Ids...>&) {
+  return std::make_tuple(fn(std::get<Ids>(tup))...);
+}
+
+/// Callable::operator()(T) cannot return void or you will get weird errors.
+template <class... Args, class Callable, class Tup = std::tuple<Args...>>
+constexpr auto MapTuple(Tup&& t, Callable&& fn) {
+  using Tup2 = typename std::remove_reference<Tup>::type;
+  return MapTupleN(t, fn, std::make_index_sequence<std::tuple_size_v<Tup2>>());
+}
+
+// -
+
+template <class Tup>
+struct SizeofTupleArgs;
+
+// c++17 fold expressions make this easy, once we pull out the Args parameter
+// pack by constraining the default template:
+template <class... Args>
+struct SizeofTupleArgs<std::tuple<Args...>>
+    : std::integral_constant<size_t, (... + sizeof(Args))> {};
+
+static_assert(SizeofTupleArgs<std::tuple<size_t, char, char, char>>::value ==
+              sizeof(size_t) + 3);
+
+}  // namespace mozilla
+
+#endif  // DOM_CANVAS_TUPLE_UTILS_H