Re: [boost] Seeking advice regarding inline namespaces

Subject: Re: [boost] Seeking advice regarding inline namespaces
From: Louis Dionne (ldionne.2_at_[hidden])
Date: 2015-11-12 20:26:05

> On 13/11/2015 01:24, Louis Dionne wrote:
> > Ok, but since L can't guarantee ABI compatibility at all between
> versions,
> > this means that such a version namespace must change between each
> version
> > to ensure that you get a linker error even between v1.0.0 and v1.0.1,
> > correct? In other words, what you want is
> >
> > Version 1.0.0:
> >
> >      namespace L { inline namespace v1_0_0 { } }
> >
> >
> > Version 1.0.1:
> >
> >      namespace L { inline namespace v1_0_1 { } }
> >
> > Version 1.0.2:
> >
> >      namespace L { inline namespace v1_0_2 { } }
> >
> >
> > ... and so on, for literally each released version of the library L.
> >
> > Is this correct?
> 
> Yes, if you want to provide that feature to your users, then that's how 
> to do it.  Typically you'd have a macro or the namespace decls in some 
> prefix header so you don't have to repeat yourself too much.
> 
> The easiest thing to do is to provide a common version namespace for 
> everything, but you could instead decide to version each type 
> individually and increment them only when actually modified.
> 
> There are other things you can do to reduce potential ABI breakage, such 
> as using #pragma pack.  This is less important for most consumers, 
> though, as most apps don't play with the packing.
> 
> There are also other compiler settings you can take into account in your 
> namespace name when you know that they affect ABI, eg. whether 
> exceptions are enabled or not.  I can't think of a specific example at 
> the moment but I know at least one Boost library does this.

Ok, thanks a lot for the information. Keeping this in mind, I'll consider 
whether the added complexity of versionning Hana's namespace seems to be 
worth it (given the nature of Hana as a metaprogramming library).

Regards,
Louis

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