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 07:24:55

> On 12/11/2015 06:26, Louis Dionne wrote:
>
> > [...]
> > (2) Assuming that it is unreasonable for a library L to guarantee ABI
> >      compatibility from one version to the next, would there still be a
> >      reason to use inline namespaces to version that library?
> 
> Yes, this is the best reason to do so.  Imagine a static library A that 
> has been built against version 1 of L, and then an application that is 
> trying to consume version 2 of L and the prebuilt library A.
> 
> Without version-specific namespaces, there is a very good chance that 
> this will successfully link, but then fail in some unspecified (and 
> probably horrible, or worse: subtle) way at runtime.  With 
> version-specific namespaces, this will fail to link until the user 
> either switches the application to use v1 of L or rebuilds A to use v2 
> as well.
> 
> The above assumes that v2 of L does not define the namespace that v1 
> used.  If instead v2 defined "ABI compatible symbols" in a v1-named 
> namespace as well (which is harder), then the above scenario *might* 
> link and even work correctly, assuming that either the app and lib A did 
> not pass lib L's objects to each other, or that lib L defined ways to 
> make them interoperable (which can also be hard).

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?

Regards,
Louis

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