Re: [boost] [system] Why is this not header-only?

From: Jeff Garland (jeff_at_[hidden])
Date: 2007-04-03 12:41:33

Julio M. Merino Vidal wrote:
> On 02/04/2007, at 19:11, Andrey Semashev wrote:
> 
>> Although the discussion is slipping away from the original question, I
>> must say I 100% agree with Jeff. The best solution is to give user a
>> choice whether to link or to go header-only (where possible). And in
>> my opinion such solution should be unified for all boost libs.
>> We already have the BOOST_USE_WINDOWS_H macro, why not extend it to
>> something like BOOST_USE_OS_NATIVE_HEADERS? I think this would settle
>> the problem once and for all. The only problem is I'm not sure how
>> such a transition should be organized.
> 
> Although I liked this at first too, it seems to me it cannot be  
> always implemented.  I was now trying to add a singleton to my  
> library and I can't do it with headers alone.   

oh, oh...

> I need to maintain  
> the pointer to the global instance somewhere, and that means having a  

because?

> global variable which cannot be defined in a header (or otherwise  
> you'll get duplicates).  Unless I'm missing something, that is...
> 

Moving it to a library won't solve all the problems either -- you'll be 
constrained to a dll on windows to guarantee a singleton unless you jump 
through some big hoops (thread lib had this problem -- still does AFAIK).  The 
problem comes about if 2 dll's link with your static lib...they'll create 2 
copies of you singleton at dll init time.

Really, I'd rethink the singleton design if at all possible.

Jeff