Add attributes

examples/src/attributes.cpp

@@ -0,0 +1,27 @@
+#include <utempl/attributes.hpp>
+#include <string>
+
+template <typename T>
+struct AttributeData {
+  T value;
+};
+
+
+#define MY_ATTRIBUTE(type, ...) GENERIC_ATTRIBUTE(AttributeData<type>{__VA_ARGS__})
+
+
+ATTRIBUTE_STRUCT(SomeStruct, 
+  MY_ATTRIBUTE(int, .value = 2);
+  int field;
+  SKIP_ATTRIBUTE();
+  int field2;
+  MY_ATTRIBUTE(std::string, .value = "HEY!")
+  std::string field3;
+);
+
+static_assert(SomeStruct::GetAttribute<0>().value == 2);
+static_assert(SomeStruct::GetAttribute<2>().value == "HEY!");
+
+
+
+auto main() -> int {};

examples/src/make.cpp

@@ -0,0 +1,5 @@
+#include <utempl/utils.hpp>
+
+auto main() -> int {
+  constexpr auto arr = utempl::TupleMaker<std::array<void*, 0>>::Make();
+};

include/utempl/attributes.hpp

@@ -0,0 +1,48 @@
+#include <utempl/loopholes/counter.hpp>
+#include <utempl/meta_info.hpp>
+
+
+namespace utempl {
+
+
+
+namespace impl {
+
+struct AttributesTag {};
+
+template <typename T>
+struct AttributesCounterTag {};
+
+
+template <typename Current, auto f = []{}, auto = AddTypeToTag<impl::AttributesTag, Current, decltype(f)>()>
+struct CurrentSetter {};
+
+
+} // namespace impl
+
+
+
+
+
+#define ATTRIBUTE_STRUCT(name, ...) struct name { \
+static_assert((::utempl::impl::CurrentSetter<name>(), true)); \
+template <std::size_t N> \
+static consteval auto GetAttribute(); __VA_ARGS__ }
+
+struct NoInfo {};
+
+#define GENERIC_ATTRIBUTE(value) \
+  template <> \
+  consteval auto GetAttribute< \
+      ::utempl::loopholes::Counter< \
+        ::utempl::impl::AttributesCounterTag<decltype(::utempl::GetCurrentTagType< \
+          ::utempl::impl::AttributesTag, \
+          decltype([]{}) \
+        >())::Type \
+      >, \
+      decltype([]{}) >()>() { return value; }
+
+#define SKIP_ATTRIBUTE() GENERIC_ATTRIBUTE(::utempl::NoInfo{})
+
+
+} // namespace utempl

include/utempl/meta_info.hpp

@@ -70,6 +70,16 @@ consteval auto GetTypeListForTag() {
   return impl::GetTypeListForTag<Tag>(TypeList<Ts...>{});
 };
 
+template <
+  typename Tag,
+  typename... Ts,
+  auto I = utempl::loopholes::CountValue<Tag, Ts...>() - 1
+>
+consteval auto GetCurrentTagType() {
+  return Magic(utempl::loopholes::Getter<MetaInfoKey<I, Tag>{}>());
+};
+
+
 /*
 static_assert(kTypeId<int> == 0);
 static_assert(kTypeId<void> == 1);