From 9186051642e972a584c3bd9514d3ff8f10e7b8a0 Mon Sep 17 00:00:00 2001
From: Yaraslau Tamashevich <yaraslau.tamashevich@gmail.com>
Date: Thu, 12 Dec 2024 12:41:15 +0200
Subject: [PATCH] Fixes problem of working on structs with only a single
 element

---
 include/reflection-cpp/reflection.hpp |  4 ++--
 test-reflection-cpp.cpp               | 28 ++++++++++++++++++++++++++-
 2 files changed, 29 insertions(+), 3 deletions(-)

diff --git a/include/reflection-cpp/reflection.hpp b/include/reflection-cpp/reflection.hpp
index 9ac6424..c2b6e61 100644
--- a/include/reflection-cpp/reflection.hpp
+++ b/include/reflection-cpp/reflection.hpp
@@ -715,7 +715,7 @@ constexpr void EnumerateMembers(Callable&& callable)
 }
 
 template <typename Object, typename Callable>
-    requires std::same_as<void, std::invoke_result_t<Callable, std::string, MemberTypeOf<1, Object>>>
+    requires std::same_as<void, std::invoke_result_t<Callable, std::string, MemberTypeOf<0, Object>>>
 void CallOnMembers(Object& object, Callable&& callable)
 {
     EnumerateMembers<Object>(object,
@@ -752,7 +752,7 @@ constexpr ResultType FoldMembers(ResultType initialValue, Callable const& callab
 ///
 /// @return The result of the fold
 template <typename Object, typename Callable, typename ResultType>
-    requires std::same_as<ResultType, std::invoke_result_t<Callable, std::string, MemberTypeOf<1, Object>, ResultType>>
+    requires std::same_as<ResultType, std::invoke_result_t<Callable, std::string, MemberTypeOf<0, Object>, ResultType>>
 constexpr ResultType FoldMembers(Object& object, ResultType initialValue, Callable const& callable)
 {
     // clang-format off
diff --git a/test-reflection-cpp.cpp b/test-reflection-cpp.cpp
index 607cac2..4029687 100644
--- a/test-reflection-cpp.cpp
+++ b/test-reflection-cpp.cpp
@@ -30,6 +30,11 @@ enum Color
     Blue
 };
 
+struct SingleValueRecord
+{
+    int value;
+};
+
 TEST_CASE("GetName", "[reflection]")
 {
     auto const enumValue = Reflection::GetName<Color::Red>();
@@ -38,13 +43,34 @@ TEST_CASE("GetName", "[reflection]")
     auto const enumValue2 = Reflection::GetName<Color::Green>();
     CHECK(enumValue2 == "Green");
 
-    auto const person = Person { "John Doe", "john@doe.com", 42 };
     auto const memberName1 = Reflection::GetName<&Person::email>();
     CHECK(memberName1 == "email");
+
+    auto const singleValueField = Reflection::GetName<&SingleValueRecord::value>();
+    CHECK(singleValueField == "value");
+}
+
+TEST_CASE("single value record", "[reflection]")
+{
+    static_assert(Reflection::CountMembers<SingleValueRecord> == 1);
+
+    auto const s = SingleValueRecord { 42 };
+    auto const t = Reflection::ToTuple(s);
+
+    CHECK(std::get<0>(t) == 42);
+    CHECK(Reflection::GetMemberAt<0>(s) == 42);
+
+    Reflection::CallOnMembers(s, [](auto&& name, auto&& value) {
+        CHECK(name == "value");
+        CHECK(value == 42);
+    });
 }
 
 TEST_CASE("core", "[reflection]")
 {
+    auto s = SingleValueRecord { 42 };
+    CHECK(Reflection::Inspect(s) == "value=42");
+
     auto p = Person { "John Doe", "john@doe.com", 42 };
     auto const result = Reflection::Inspect(p);
     CHECK(result == R"(name="John Doe" email="john@doe.com" age=42)");