-----Original Message----- From: boost-bounces@lists.boost.org [mailto:boost-bounces@lists.boost.org] On Behalf Of Peter Dimov Sent: Monday, February 14, 2005 4:27 PM To: boost@lists.boost.org Subject: Re: [boost] singleton usage
Jorge Lodos wrote:
Thank you for your comments. I agree with everything you said and try to avoid singletons in the first place. However, I have a practical problem that I have been able to "solve" only thru singletons. In a header only library that uses a class factory, the registration of objects with the factory is performed in a constructor of an object inside an anonymous namespace. Since the header may be #included more that once, I made those objects singletons to avoid multiple registration. The singleton::instance method may be called more that once without need, that's why I put "solve" in quotes. Since the object is inside an anonymous namespace, I can not use templates, which never get instantiated. If you or anyone else have a suggestion that allows for automatic registration without using singletons please share it :-)
Can you use something like the following:
class auto_reg { static int count_;
auto_reg() { if( ++count_ == 1 ) register(); }
~auto_reg() { if( --count_ == 0 ) unregister(); } };
int auto_reg::count_;
To make it header-only use the template<class _ = void> trick.
Well, this sure would replace the singletons, thanks! Still, the class constructor will be called more than once. I was hoping there was a solution where this wouldn't happen. Some template magic, I guess :-). Thanks again! Jorge Jorge