From c7177adc21993307482b2c18dc4db6a03361586d Mon Sep 17 00:00:00 2001
From: Mikko Rasa <tdb@tdb.fi>
Date: Sat, 5 Nov 2022 00:40:55 +0200
Subject: [PATCH] Add a way for systems to do things at the end of a tick

Objects should not be created or destroyed mid-tick.
---
 source/game/stage.cpp  |  2 ++
 source/game/system.cpp | 12 ++++++++++++
 source/game/system.h   |  7 +++++++
 3 files changed, 21 insertions(+)
 create mode 100644 source/game/system.cpp

diff --git a/source/game/stage.cpp b/source/game/stage.cpp
index 1c56c7e..8317610 100644
--- a/source/game/stage.cpp
+++ b/source/game/stage.cpp
@@ -39,6 +39,8 @@ void Stage::tick(Time::TimeDelta dt)
 {
 	for(const auto &s: systems)
 		s->tick(dt);
+	for(const auto &s: systems)
+		s->deferred_tick();
 }
 
 } // namespace Msp::Game
diff --git a/source/game/system.cpp b/source/game/system.cpp
new file mode 100644
index 0000000..87ba3b6
--- /dev/null
+++ b/source/game/system.cpp
@@ -0,0 +1,12 @@
+#include "system.h"
+
+namespace Msp::Game {
+
+void System::deferred_tick()
+{
+	for(const auto &f: deferred_queue)
+		f();
+	deferred_queue.clear();
+}
+
+} // namespace Msp::Game
diff --git a/source/game/system.h b/source/game/system.h
index 9e6ec2a..3b37917 100644
--- a/source/game/system.h
+++ b/source/game/system.h
@@ -1,6 +1,7 @@
 #ifndef MSP_GAME_SYSTEM_H_
 #define MSP_GAME_SYSTEM_H_
 
+#include <functional>
 #include <msp/time/timedelta.h>
 
 namespace Msp::Game {
@@ -11,6 +12,7 @@ class System
 {
 protected:
 	Stage &stage;
+	std::vector<std::function<void()>> deferred_queue;
 
 	System(Stage &s): stage(s) { }
 public:
@@ -19,6 +21,11 @@ public:
 	Stage &get_stage() const { return stage; }
 
 	virtual void tick(Time::TimeDelta) = 0;
+	virtual void deferred_tick();
+
+protected:
+	template<typename F>
+	void defer(F &&f) { deferred_queue.emplace_back(std::forward<F>(f)); }
 };
 
 } // namespace Msp::Game
-- 
2.43.0