Implement CollectDifferences

include/reflection-cpp/reflection.hpp

@@ -811,6 +811,25 @@ std::string Inspect(std::vector<Object> const& objects)
     }
     return str;
 }
+
+template <typename Object, typename Callback>
+void CollectDifferences(const Object& lhs, const Object& rhs, Callback&& callback)
+{
+    template_for<0, CountMembers<Object>>([&]<auto I>() {
+        if constexpr (std::equality_comparable<MemberTypeOf<I, Object>>)
+        {
+            if (GetMemberAt<I>(lhs) != GetMemberAt<I>(rhs))
+            {
+                callback(MemberNameOf<I, Object>, GetMemberAt<I>(lhs), GetMemberAt<I>(rhs));
+            }
+        }
+        else
+        {
+            CollectDifferences(GetMemberAt<I>(lhs), GetMemberAt<I>(rhs), callback);
+        }
+    });
+}
+
 } // namespace Reflection
 
 template <std::size_t N>

test-reflection-cpp.cpp

@@ -102,3 +102,53 @@ TEST_CASE("MemberTypeOf", "[reflection]")
     static_assert(std::same_as<Reflection::MemberTypeOf<3, TestStruct>, std::string>);
     static_assert(std::same_as<Reflection::MemberTypeOf<4, TestStruct>, Person>);
 }
+
+struct Record
+{
+    int id;
+    std::string name;
+    int age;
+};
+
+TEST_CASE("Compare.simple", "[reflection]")
+{
+    auto const r1 = Record { .id = 1, .name = "John Doe", .age = 42 };
+    auto const r2 = Record { .id = 1, .name = "John Doe", .age = 42 };
+    auto const r3 = Record { .id = 2, .name = "Jane Doe", .age = 43 };
+
+    std::string diff;
+    auto differenceCallback = [&](std::string_view name, auto const& lhs, auto const& rhs) {
+        diff += std::format("{}: {} != {}\n", name, lhs, rhs);
+    };
+
+    Reflection::CollectDifferences(r1, r2, differenceCallback);
+    CHECK(diff.empty());
+    Reflection::CollectDifferences(r1, r3, differenceCallback);
+    CHECK(diff == "id: 1 != 2\nname: John Doe != Jane Doe\nage: 42 != 43\n");
+}
+
+struct Table
+{
+    Record first;
+    Record second;
+};
+
+TEST_CASE("Compare.nested", "[reflection]")
+{
+    auto const t1 = Table { .first = { .id = 1, .name = "John Doe", .age = 42 },
+                            .second = { .id = 2, .name = "Jane Doe", .age = 43 } };
+    auto const t2 = Table { .first = { .id = 1, .name = "John Doe", .age = 42 },
+                            .second = { .id = 2, .name = "Jane Doe", .age = 43 } };
+    auto const t3 = Table { .first = { .id = 1, .name = "John Doe", .age = 42 },
+                            .second = { .id = 3, .name = "Jane Doe", .age = 43 } };
+
+    std::string diff;
+    auto differenceCallback = [&](std::string_view name, auto const& lhs, auto const& rhs) {
+        diff += std::format("{}: {} != {}\n", name, lhs, rhs);
+    };
+
+    Reflection::CollectDifferences(t1, t2, differenceCallback);
+    CHECK(diff.empty());
+    Reflection::CollectDifferences(t1, t3, differenceCallback);
+    CHECK(diff == "id: 2 != 3\n");
+}