Add MapType capability for TypePack

src/pbrt/util/containers.h

@@ -101,6 +101,18 @@ struct TakeFirstN<1, TypePack<T, Ts...>> {
     using type = TypePack<T>;
 };
 
+template <template <typename> class M, typename... Ts>
+struct MapType;
+template <template <typename> class M, typename T>
+struct MapType<M, TypePack<T>> {
+    using type = TypePack<M<T>>;
+};
+
+template <template <typename> class M, typename T, typename... Ts>
+struct MapType<M, TypePack<T, Ts...>> {
+    using type = typename Prepend<M<T>, typename MapType<M, TypePack<Ts...>>::type>::type;
+};
+
 template <typename F, typename... Ts>
 void ForEachType(F func, TypePack<Ts...>);
 template <typename F, typename T, typename... Ts>

src/pbrt/util/containers_test.cpp

@@ -128,3 +128,24 @@ TEST(TypePack, HasType) {
     EXPECT_FALSE((HasType<char, Pack>::value));
     EXPECT_FALSE((HasType<unsigned int, Pack>::value));
 }
+
+TEST(TypePack, TakeRemove) {
+    using Pack = TypePack<signed int, float, double>;
+
+    static_assert(std::is_same_v<TypePack<signed int>, typename TakeFirstN<1, Pack>::type>);
+    static_assert(std::is_same_v<TypePack<float>, typename TakeFirstN<1, typename RemoveFirstN<1, Pack>::type>::type>);
+    static_assert(std::is_same_v<TypePack<double>, typename TakeFirstN<1, typename RemoveFirstN<2, Pack>::type>::type>);
+}
+
+template <typename T> struct Set { };
+
+TEST(TypePack, Map) {
+    using SetPack = typename MapType<Set, TypePack<signed int, float, double>>::type;
+
+    static_assert(std::is_same_v<TypePack<Set<signed int>>,
+                  typename TakeFirstN<1, SetPack>::type>);
+    static_assert(std::is_same_v<TypePack<Set<float>>,
+                  typename TakeFirstN<1, typename RemoveFirstN<1, SetPack>::type>::type>);
+    static_assert(std::is_same_v<TypePack<Set<double>>,
+                  typename TakeFirstN<1, typename RemoveFirstN<2, SetPack>::type>::type>);
+}