From 604b4ae5720836cb4ee9a66085d3290067c63c84 Mon Sep 17 00:00:00 2001
From: Stanislaw Halik <sthalik@misaki.pl>
Date: Tue, 15 Nov 2022 09:19:04 +0100
Subject: entity: add visit_tuple

---
 src/entity.hpp  | 26 +++++++++++++++++++++++++-
 test/entity.cpp | 28 ++++++++++++++++++++++++----
 2 files changed, 49 insertions(+), 5 deletions(-)

diff --git a/src/entity.hpp b/src/entity.hpp
index 1c055ce7..ba165662 100644
--- a/src/entity.hpp
+++ b/src/entity.hpp
@@ -1,9 +1,10 @@
 #pragma once
 #include "compat/integer-types.hpp"
-#include <Corrade/Containers/StringView.h>
 #include <concepts>
 #include <compare>
 #include <type_traits>
+#include <utility>
+#include <Corrade/Containers/StringView.h>
 
 namespace floormat {}
 
@@ -128,6 +129,29 @@ struct Entity final {
     };
 };
 
+namespace detail {
+template<typename F, typename Tuple, std::size_t N>
+requires std::invocable<F, decltype(std::get<N>(std::declval<Tuple>()))>
+constexpr CORRADE_ALWAYS_INLINE void visit_tuple(F&& fun, Tuple&& tuple)
+{
+    using Size = std::tuple_size<std::decay_t<Tuple>>;
+    static_assert(N < Size());
+
+    fun(std::get<N>(tuple));
+    if constexpr(N+1 < Size())
+        visit_tuple<F, Tuple, N+1>(std::forward<F>(fun), std::forward<Tuple>(tuple));
+}
+
+} // namespace detail
+
+template<typename F, typename Tuple>
+constexpr void visit_tuple(F&& fun, Tuple&& tuple)
+{
+    using Size = std::tuple_size<std::decay_t<Tuple>>;
+    if constexpr(Size() > 0)
+        detail::visit_tuple<F, Tuple, 0>(std::forward<F>(fun), std::forward<Tuple>(tuple));
+}
+
 enum class erased_field_type : std::uint32_t {
     none,
     string,
diff --git a/test/entity.cpp b/test/entity.cpp
index 80032b6f..21783e24 100644
--- a/test/entity.cpp
+++ b/test/entity.cpp
@@ -1,13 +1,14 @@
 #include "app.hpp"
 #include "compat/assert.hpp"
 #include "src/entity.hpp"
+#include <tuple>
 
 using namespace floormat;
 using namespace floormat::entities;
 
 struct TestAccessors {
-    int bar() const { return _bar; }
-    void set_bar(int value) { _bar = value; }
+    constexpr int bar() const { return _bar; }
+    constexpr void set_bar(int value) { _bar = value; }
     int foo;
     int _bar;
     int _baz;
@@ -22,7 +23,7 @@ static constexpr auto m_baz = entity::type<int>::field("baz"_s, r_baz, w_baz);
 
 namespace floormat {
 
-static void test_accessors()
+static constexpr bool test_accessors()
 {
     auto x = TestAccessors{111, 222, 333};
 
@@ -38,11 +39,30 @@ static void test_accessors()
         auto a = m_foo.read(x), b = m_bar.read(x), c = m_baz.read(x);
         fm_assert(a == 1111 && b == 2222 && c == 3333);
     }
+    return true;
+}
+
+static constexpr bool test_visitor()
+{
+    {
+        int ret = 0;
+        visit_tuple([&](auto x) { ret += x; },
+                    std::tuple<int, short, char, long>{ 1, 2, 3, 4 });
+        fm_assert(ret == 1 + 2 + 3 + 4);
+    }
+    {
+        int ret = 0;
+        visit_tuple([&] { ret++; }, std::tuple<>{});
+        fm_assert(ret == 0);
+    }
+
+    return true;
 }
 
 void test_app::test_entity()
 {
-    test_accessors();
+    static_assert(test_accessors());
+    static_assert(test_visitor());
 }
 
 } // namespace floormat
-- 
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