So, how do I define a prototype for an object (struct, class, enum, etc..) that is hidden in a namespace? I've seriously tried pretty much everything.. Here is a simplified example: namespace MsgBox { enum Type {TOK,TYesNo}; enum Answer {AOK,AYes,ANo}; } // ... class IWinApp { public: MsgBox::Answer MsgBox(MsgBox::Type,char * Txt,...); // ... }; This works, but the namespace "MsgBox" has to be defined before anything using stuff in it. This is not a serious problem for my project but I'm just curious.. Anyway, Is there a way to define a prototype for a namespace? That should solve it.. [Edited by - tmunq on May 26, 2005 1:37:24 PM]

Well, not really - the compiler needs to know what a "MsgBox::Type" before it can be used, independent of which namespace it resides in. A class/struct/union you could forward declare in a namespace, like this:

namespace foo { class bar; }

but enums cannot be forward declared -- and even if they could, you could only declare pointers and references to them, not use them, the same way as with classes.

Thanks, Fruny. That is close enough to a prototype. :)

namespace MsgBox
{
enum Answer;
enum Type;
enum Picture;
}

// ...

class IWinApp
{
public:
// Displays a message box
virtual MsgBox::Answer MsgBox(MsgBox::Type Type,MsgBox::Picture Pic,char * Txt,...) = 0;
// ...
};

namespace MsgBox
{
enum Answer {AOK,AYes,ANo,ACancel,ARetry,AIgnore};
//...

This seems to work..

An enum is a user-defined type, just like a class, so there's no reason you can't do this.. (in fact, you can overload operators on enums as well.. though that's not really relevant)

My question is, why would you wish to do this?

I suppose one reason would be to marginally improve compilation time, but that depends on your source-include structure.

I guess you could also use this to place the actual definition of the enum in a .cpp file, though I hardly think that's worth it.. you're just defining constants, and the compiled output will be identical either way.

My argument would be to define it in one place.. if I want to look up the enum's definition, I only have to look at one spot, instead of seeing the declaration and then trying to hunt down the definition.