Reduced the number of explicit retain/release method calls on love objects. Less chance of bugs!

src/modules/physics/box2d/Body.cpp

@@ -41,7 +41,6 @@ Body::Body(World *world, b2Vec2 p, Body::Type type)
 {
 	udata = new bodyudata();
 	udata->ref = nullptr;
-	world->retain();
 	b2BodyDef def;
 	def.position = Physics::scaleDown(p);
 	def.userData = (void *) udata;
@@ -57,8 +56,7 @@ Body::Body(b2Body *b)
 	, udata(nullptr)
 {
 	udata = (bodyudata *) b->GetUserData();
-	world = (World *)Memoizer::find(b->GetWorld());
-	world->retain();
+	world.set((World *) Memoizer::find(b->GetWorld()));
 	// Box2D body holds a reference to the love Body.
 	this->retain();
 	Memoizer::add(body, this);
@@ -69,7 +67,6 @@ Body::~Body()
 	if (udata != nullptr)
 		delete udata->ref;
 	delete udata;
-	world->release();
 }
 
 float Body::getX()
@@ -420,7 +417,7 @@ bool Body::isFixedRotation() const
 
 World *Body::getWorld() const
 {
-	return world;
+	return world.get();
 }
 
 int Body::getFixtureList(lua_State *L) const

src/modules/physics/box2d/Body.h

@@ -436,7 +436,7 @@ private:
 	//
 	// This ensures that a World only can be destroyed
 	// once all bodies have been destroyed too.
-	World *world;
+	Object::StrongRef<World> world;
 
 	bodyudata *udata;
 

src/modules/physics/box2d/Joint.cpp

@@ -40,7 +40,7 @@ namespace box2d
 {
 
 Joint::Joint(Body *body1)
-	: world(body1->world)
+	: world(body1->world.get())
 	, udata(nullptr)
 	, body1(body1)
 	, body2(nullptr)
@@ -50,7 +50,7 @@ Joint::Joint(Body *body1)
 }
 
 Joint::Joint(Body *body1, Body *body2)
-	: world(body1->world)
+	: world(body1->world.get())
 	, udata(nullptr)
 	, body1(body1)
 	, body2(body2)

src/modules/physics/box2d/World.cpp

@@ -259,23 +259,20 @@ void World::update(float dt)
 	world->Step(dt, 8, 6);
 
 	// Destroy all objects marked during the time step.
-	for (auto i = destructBodies.begin(); i < destructBodies.end(); i++)
+	for (Body *b : destructBodies)
 	{
-		Body *b = *i;
 		if (b->body != 0) b->destroy();
 		// Release for reference in vector.
 		b->release();
 	}
-	for (auto i = destructFixtures.begin(); i < destructFixtures.end(); i++)
+	for (Fixture *f : destructFixtures)
 	{
-		Fixture *f = *i;
 		if (f->isValid()) f->destroy();
 		// Release for reference in vector.
 		f->release();
 	}
-	for (auto i = destructJoints.begin(); i < destructJoints.end(); i++)
+	for (Joint *j : destructJoints)
 	{
-		Joint *j = *i;
 		if (j->isValid()) j->destroyJoint();
 		// Release for reference in vector.
 		j->release();