Re: [Boost-users] Header file granularity policy?

From: Jeff Garland (jeff_at_[hidden])
Date: 2006-08-20 10:28:50

Robert Ramey wrote:
> Jeff Garland wrote:
> 
>>> Is there some kind of Boost convention or policy
>>> on whether a library should offer a comprehensive "declare
>>> everything in the library" header in addition to more targeted
>>> headers?
> 
> Personally, I avoid the "comprehensive" headers.  I personally
> feel uncomfortable with the idea if including unused stuff
> as a side effect.  This is especially true now that this
> extra stuff may include templates.

Hmm, most template code amounts to nothing other than a slightly slower 
compile if you don't instantiate it.  That's certainly the case for date-time.

> This is one reason that the serialization library has no such
> "comprehensive" header defined.  The other reason is that
> it's not clear how much such a header might include - all
> possible archives? all stl serialization. etc.  Finally, at
> least in the serialization library, the mere inclusion of
> a header can result in the instantiation of code which
> is never called - thereby adding to code bloat.

I think a few years ago I would have agreed with this, but I think the "size" 
issues just don't apply that much on modern machines.

> So, I think the issue would be best addressed by discouraging
> the creation and usage of "comprehensive" headers.  Of
> course, for me that is not a big issue as I avoid their usage
> in any case.

> Now, that does raise the issue that sometimes a compilation
> error arise for the lack of a specific header and that the
> error message is non-obvious.  I'm not sure, but
> perhaps this can be alleviated by more/better usage
> of concept checking in library headers.

I don't see how...

I think the ultimate cost is minimal -- a simple statement in the docs 
explaining the costs in the docs and the same as a comment in the 
comprehensive header.  As long as the fine grain headers are available those 
can continue to be used.

Jeff