Add GoInterface

include/utempl/go_interface.hpp

@@ -0,0 +1,78 @@
+#pragma once
+#include <utempl/constexpr_string.hpp>
+#include <boost/pfr.hpp>
+#include <type_traits>
+
+namespace utempl {
+
+template <ConstexprString name, typename T>
+consteval auto FindField() -> std::size_t {
+  constexpr auto names = boost::pfr::names_as_array<std::remove_cvref_t<T>>();
+  return std::ranges::find(names, static_cast<std::string_view>(name)) - names.begin();
+};
+
+template <ConstexprString name, typename T>
+inline constexpr auto Get(T&& arg) {
+  return boost::pfr::get<FindField<name, T>()>(std::forward<T>(arg));
+};
+
+template <auto...>
+struct EmptyField {};
+
+namespace impl {
+
+
+template <ConstexprString name, typename T>
+inline constexpr auto TryGet(T&& arg) 
+      -> decltype(boost::pfr::get<FindField<name, T>()>(std::forward<T>(arg)))
+      requires(FindField<name, T>() < boost::pfr::tuple_size_v<std::remove_cvref_t<T>>) {
+  constexpr auto I = FindField<name, T>();
+  return boost::pfr::get<I>(std::forward<T>(arg));
+};
+template <ConstexprString name, typename T>
+inline constexpr auto TryGet(T&& arg) {
+  return EmptyField<name>{};
+};
+
+
+template <typename To, typename Transformer, typename From>
+inline constexpr auto Transform(Transformer&& transformer, From&& from) {
+  return [&]<auto... Is>(std::index_sequence<Is...>){
+    return To{transformer(TryGet<ConstexprString<boost::pfr::get_name<Is, To>().size() + 1>{boost::pfr::get_name<Is, To>().begin()}>(from))...};
+  }(std::make_index_sequence<boost::pfr::tuple_size_v<To>>());
+};
+
+} // impl
+
+struct DefaultFieldTransformer {
+  inline constexpr auto operator()(auto&& arg) -> auto&& {
+    return arg;
+  };
+  inline constexpr auto operator()(auto& arg) -> auto& {
+    return arg;
+  };
+  template <ConstexprString str>
+  inline constexpr auto operator()(EmptyField<str> arg) {
+    static_assert(str == "This Field Not Found");
+  };
+};
+
+template <typename Value, typename Transformer = DefaultFieldTransformer>
+struct GoInterface : Value {
+  inline constexpr GoInterface(Value&& value) : 
+      Value(std::move(value)) {};
+  inline constexpr GoInterface(const Value& value) : 
+      Value(value) {};
+  template <typename T>
+  inline constexpr GoInterface(T&& value) :
+    Value(impl::Transform<Value>(Transformer{}, std::forward<T>(value))) {};
+  inline constexpr auto operator=(const GoInterface&) -> GoInterface& = default;
+  inline constexpr auto operator=(GoInterface&&) -> GoInterface& = default;
+  inline constexpr auto operator==(const GoInterface& other) const -> bool
+        requires requires {static_cast<const Value&>(*this) == static_cast<const Value&>(other);} {
+    return static_cast<const Value&>(*this) == static_cast<const Value&>(other);
+  };
+};
+
+} // namespace utempl
+