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Forward declaration - how far to go?

Julian Watzinger · 2013-05-04T16:41:44

Hello, I'm just about to step through my code to replace some unnecessary #includes with forward declaration to speed up compile time. However, I'm looking for some advice or guideline on how far I should take this. Consider this class: #pragma once #include "GfxDef.h" #include "Render/RenderStates.h" #include "Render/StateGroup.h" namespace acl { namespace gfx { class IMesh { public: virtual ~IMesh(void) = 0 {} virtual unsigned int GetStateCount(void) const = 0; virtual const render::StateGroup** GetStates(void) const = 0; virtual const render::DrawCall& GetDraw(void) const = 0; }; } } Obviously, this interface doesn't need to know anything about eigther StageGroup or DrawCall, so forward declaration would obviously do. However I need to include the header files whenever I want to use the interface. Furthermore, if I implement a class using this interface, I can still use the (existing) forward declaration, but at some point I will need to include the header files again, probably in the application code. Whats preferable in this case? When should I use forward declaration or when should I still include header files in such a use case?

General and Gameplay Programming Programming

Started by Juliean May 02, 2013 11:46 PM

11 comments, last by Juliean 10 years, 11 months ago

Juliean

7,343

Author

May 04, 2013 03:24 PM

Okay, I see, since I'm not using that much third-party libs (just directx and some standard-libaries, of course), I'm not going through the trouble right now.

But just another question, since I'm designing my "engine" with use by other users in mind, and seperate from the game I'm developing, how would I go about that? Obviously most third-party libs I know at least offer the convenience of being able to do things like:


#include "Gui/Toolbar.h"

	//create game widget button
	gui::ToolButton* pCreate = pToolbar->AddButton(L"Frame/New.png");
	pCreate->SigReleased.Connect(this, &SceneToolbarCtrl::OnCreateGameObject);

Now with the new forward declaration method, I'd need to also include "Gui/ToolButton.h". Thats a little inconvenient, which doesn't matter for the lib itself, but should I really expect the user to include everything in advance of his compile time, or is there some prefered solution for this?

SiCrane

11,840

May 04, 2013 04:36 PM

One option is to create helper headers for each subsystem of your library. In your case, you could have a gui.h header that just includes all the other headers that have items that live in the gui namespace.

Juliean

7,343

Author

May 04, 2013 04:41 PM

Ok, that makes sense. It would still rather be considered a good design if I and my fictional team were still using the seperate headers in the actual game project, right?

Forward declaration - how far to go?

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