From ee2c9f5da033356b6901ff442749c7253e5aff45 Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Mon, 31 Mar 2025 14:59:33 +0300
Subject: [PATCH] Use a different way of determining the default transactor of
 a component

Declaring the type alias in BufferedComponent results in a transactor
for BufferedComponent<T>, which does not match the actual type used in
system dependencies.
---
 source/game/component.h  |  2 --
 source/game/system.h     |  4 ++--
 source/game/transactor.h | 12 ++++++++++++
 3 files changed, 14 insertions(+), 4 deletions(-)

diff --git a/source/game/component.h b/source/game/component.h
index 7250660..372e8d9 100644
--- a/source/game/component.h
+++ b/source/game/component.h
@@ -5,7 +5,6 @@
 #include "accessguard.h"
 #include "handle.h"
 #include "mspgame_api.h"
-#include "transactor.h"
 
 namespace Msp::Game {
 
@@ -31,7 +30,6 @@ class BufferedComponent: public Component
 {
 public:
 	using Data = T;
-	using Transactor = BasicTransactor<BufferedComponent<T>>;
 	
 private:
 	T data[2];
diff --git a/source/game/system.h b/source/game/system.h
index 51b032b..84671c2 100644
--- a/source/game/system.h
+++ b/source/game/system.h
@@ -105,9 +105,9 @@ inline void System::declare_dependency(DependencyFlags flags)
 	dep.flags = flags;
 	if constexpr(std::is_base_of_v<Component, T>)
 	{
-		if constexpr(requires{ typename T::Transactor; })
+		if constexpr(Transactable<T>)
 		{
-			dep.transactor = &stage.get_or_create_transactor<typename T::Transactor>();
+			dep.transactor = &stage.get_or_create_transactor<typename TransactorFor<T>::Type>();
 			if((flags&UPDATE)==READ_OLD)
 				dep.transact_mode = Transactor::READ;
 			else if((flags&UPDATE)==WRITE)
diff --git a/source/game/transactor.h b/source/game/transactor.h
index d278a9a..93767f3 100644
--- a/source/game/transactor.h
+++ b/source/game/transactor.h
@@ -7,6 +7,10 @@
 
 namespace Msp::Game {
 
+template<typename T>
+concept Transactable =
+	requires(T &x) { typename T::Data; x.prepare_tick(); x.commit_tick(); };
+
 class MSPGAME_API Transactor
 {
 public:
@@ -84,6 +88,14 @@ void BasicTransactor<T>::commit(Mode mode)
 		stage.iterate_objects<T>([](T &c){ c.commit_tick(); });
 }
 
+
+template<typename T>
+struct TransactorFor { using Type = BasicTransactor<T>; };
+
+template<typename T>
+	requires requires { typename T::Transactor; }
+struct TransactorFor<T> { using Type = typename T::Transactor; };
+
 } // namespace Msp::Game
 
 #endif
-- 
2.45.2