Talk:Forward declaration

That may be a good example of a "forward reference" but it's not any kind of example of a forward declaration (a topic for which the article redirects to here).

At least in C/C++, forward declaration is about declaring a symbol's type prior to specifying the full definition of that symbol, so that that symbol can be used in contexts that need only the type information and not the full definition.

A C++ example of a header file that uses forward declaration:

#ifndef SYSTEM_H
#define SYSTEM_H

class Gizmo;
class Widget;

class System 
{
public:
    const Gizmo* GetGizmo() const;
    const Widget* GetWidget() const;

private:
    const Gizmo* m_Gizmo;
    const Widget* m_Widget;
};

#endif

The point of doing this is that this header doesn't depend at all on the definitions of Gizmo and Widget. If this class directly contained a Gizmo (rather than a Gizmo pointer) then this header would need to include the header that defines a gizmo:

#include "gizmo.h"

Avoiding that header-in-header include means that fewer files will have to be recompiled when "gizmo.h" changes.

Requested move

"Forward declaration" is the first term covered in the article, and the one with an unambiguous meaning. "Forward reference" (as explained later in the article) may be a synonym of "forward declaration", or it may refer to something else. —Quuxplusone 22:05, 24 June 2007 (UTC)

This article has been renamed from forward reference to forward declaration as the result of a move request. --Stemonitis 20:14, 30 June 2007 (UTC)

Why require forward declaration?

This article does a good job of explaining what forward declaration is, but not why it exists. From reading the forward reference section I can make an educated guess that it enables faster compiling, but the article never explicitly tells me. --Tom Edwards (talk) 11:45, 17 August 2009 (UTC)