Steel Penny Games

So, during a refactor of a large section of code, I ran into an oddity with Microsoft's Visual Studio compiler in the way templates, default parameters, and namespace/class works. Really odd, particularly because it had been my (naive) understanding that a namespace and a class are quite close to the same thing if your functions are all declared to be static inside the class... truthfully, I (and most people I've talked to) believe that a class wrapping a bunch of static functions is just a nice way to force the user to use ClassName:: in front of your function calls. Well, I ran into an issue with this just a few days ago... don't recall what it was. But by running into a second one today, I thought it was worthwhile posting about it.

typedef TDelegate0<void> MyDelegate;

    void MyFunc(void)  {  }
    class C  
    {  
    public:  	
        static void Fn(MyDelegate d = MyDelegate::FromFn<myfunc>()) {} 
    };

    namespace NS  
    {
  	static void Fn(MyDelegate d = MyDelegate::FromFn<myfunc>()) {}
    };

    void main(void)
    {
        C::Fn();  // error deducing template argument
        NS::Fn(); // no problem  

}

Don't worry too much about the template typedef itself--it's basically a wrapper for a callback function. The important thing to notice is that, at least with Visual Studio 2005 SP1, these are not equivalent constructs. Of course, I only came across this when I tried to make a function take a default parameter and ran into all kinds of trouble with deducing template arguments. When I simplified the code down, I did so with a namespace (by accident) and had no trouble at all. Just changing the namespace keyword to class caused the issue to pop up. Sigh.

Why can't we have nice things?