-onBegin() return type was changed from void to bool

-disabling system execution in onBegin() funciton

source/ecs/manager.d

@@ -441,29 +441,35 @@ class EntityManager
             system.m_update = &callUpdate;
         }
 
-        static string catchFunc()(string member, string func)
+        static string catchFunc(RetType = void)(string member, string func)
         {
-            string ret = "static if (hasMember!(Sys, \"" ~ func ~ "\"))
+            //dfmt off
+            static if(is(RetType == void))string ret_str = "";
+            else string ret_str = "return ";
+            string ret = "static if (hasMember!(Sys, \"" ~ func ~ "\") && 
+                            Parameters!(Sys."~func~").length == 0 && 
+                            is(ReturnType!(Sys."~func~") == "~RetType.stringof~"))
             {
-                static void call" ~ func
+                static "~RetType.stringof~" call" ~ func
                 ~ "(void* system_pointer)
                 {
 
                     Sys* s = cast(Sys*) system_pointer;
-                    s." ~ func ~ "();
+                    "~ret_str~"s." ~ func ~ "();
                 }
 
                 system."
                 ~ member ~ " = &call" ~ func ~ ";
             }";
             return ret;
+            //dfmt on
         }
 
         mixin(catchFunc("m_enable", "onEnable"));
         mixin(catchFunc("m_disable", "onDisable"));
         mixin(catchFunc("m_create", "onCreate"));
         mixin(catchFunc("m_destroy", "onDestroy"));
-        mixin(catchFunc("m_begin", "onBegin"));
+        mixin(catchFunc!(bool)("m_begin", "onBegin"));
         mixin(catchFunc("m_end", "onEnd"));
 
         system.m_system_pointer = cast(void*) Mallocator.instance.make!Sys;
@@ -654,7 +660,7 @@ class EntityManager
             foreach (caller; passes[pass].system_callers)
             {
                 System* sys = &systems[caller.system_id];
-                if (sys.enabled)
+                if (sys.enabled && sys.execute)
                 {
                     //if (sys.m_begin)
                     //    sys.m_begin(sys.m_system_pointer);
@@ -704,7 +710,7 @@ class EntityManager
         foreach (caller; passes[pass].system_callers)
         {
             System* sys = &systems[caller.system_id];
-            if (sys.enabled)
+            if (sys.enabled && sys.execute)
             {
                 uint entities_count = 0;
                 foreach (info; caller.infos)
@@ -1668,10 +1674,10 @@ class EntityManager
         commit();
         m_call_data_allocator.clear();
 
-        foreach (ref system; instance.systems)
+        foreach (ref system; systems)
         {
-            if (system.m_begin)
-                (cast(void function(void*)) system.m_begin)(system.m_system_pointer);
+            if (system.enabled && system.m_begin)
+                system.execute = (cast(bool function(void*)) system.m_begin)(system.m_system_pointer);
         }
     }
 
@@ -1681,9 +1687,9 @@ class EntityManager
     export void end()
     {
 
-        foreach (ref system; instance.systems)
+        foreach (ref system; systems)
         {
-            if (system.m_end)
+            if (system.enabled && system.m_end)
                 (cast(void function(void*)) system.m_end)(system.m_system_pointer);
         }
 
@@ -1715,8 +1721,8 @@ class EntityManager
             }
             uint index = 0;
             SystemCaller*[] exclusion;
-            exclusion = (cast(SystemCaller**) alloca((SystemCaller*).sizeof * pass.system_callers.length))[0
-                .. pass.system_callers.length];
+            exclusion = (cast(SystemCaller**) alloca((SystemCaller*)
+                    .sizeof * pass.system_callers.length))[0 .. pass.system_callers.length];
             foreach (caller; pass.system_callers)
             {
                 index = 0;
@@ -1787,8 +1793,8 @@ class EntityManager
                     return 1;
             }
 
-            qsort(pass.system_callers.array.ptr, pass.system_callers.length, (SystemCaller*)
-                    .sizeof, &compareSystems);
+            qsort(pass.system_callers.array.ptr, pass.system_callers.length,
+                    (SystemCaller*).sizeof, &compareSystems);
 
             /*static struct CallerData
             {
@@ -1830,7 +1836,8 @@ class EntityManager
                 if (index > 0)
                 {
                     caller.dependencies = Mallocator.instance.makeArray(exclusion[0 .. index]);
-                    caller.job_group.dependencies = Mallocator.instance.makeArray!(JobGroup*)(index);
+                    caller.job_group.dependencies = Mallocator.instance.makeArray!(
+                            JobGroup*)(index);
 
                     foreach (j, dep; caller.dependencies)
                     {
@@ -2015,8 +2022,10 @@ class EntityManager
         ~this()
         {
             assert(name);
-            if(name)Mallocator.instance.dispose(name);
+            if (name)
+                Mallocator.instance.dispose(name);
         }
+
         char[] name;
         Vector!(SystemCaller*) system_callers;
     }

source/ecs/system.d

@@ -47,6 +47,9 @@ struct System
 
 package:
 
+    ///should system be executed in current update?
+    bool execute = true;
+
     ///should system update and catch events?
     bool m_enabled = false;
     ///system priority

tests/tests.d

@@ -111,9 +111,10 @@ int main()
 			writeln("On Test System destroy.");
 		}
 
-		void onBegin()
+		bool onBegin()
 		{
 			//writeln("On Test System begin.");
+			return true;
 		}
 
 		void onEnd()