Niall Douglas
On 27 Aug 2015 at 12:54, Roland Bock wrote:
c) There are older versions in there. There is 1.3 and 1.4 at least (are there more?). Please choose one. Go for it.
AFIO provides strong ABI and API evolution guarantees. It guarantees that if you compile and link to v2 of the ABI, your code will continue to compile and link no matter what changes next in AFIO.
I think we all very much appreciate backwards compatibility guarantees (and indeed the lack of this in almost all C++ libraries, Boost included, can be quite annoying), but of course they do imply added size and complexity. My understanding is that AFIO, being a new library, doesn't have any existing users (except perhaps some of your own unpublished code, but that doesn't make for a very compelling justification) and therefore there is no benefit in providing backwards compatibility with prior versions of AFIO. It seems what you are trying to do is provide a demonstration of the way backwards compatibility will work for future versions of AFIO, when it would actually be useful, and also perhaps to provide an example of a good design for supporting backwards compatibility in C++ libraries. While this is interesting, perhaps it would be better to do this as an example separate from AFIO, so that AFIO can remain as small and simple as possible. One comment on this design: it seems that different version of AFIO will function as completely independent libraries, that can each be used independently. While this is certainly much better than what most C++ libraries provide, there is still the potential for AFIO version incompatibilities: one piece of code (A) may rely on version X of AFIO but also needs to interoperate (via AFIO types) with another piece of code (B) that formerly relied on AFIO version X, but upgraded to AFIO version X+1. Ideally the backwards/forwards compatibility would be finer-grained, so that this interoperability might be possible, but of course that tends to severely constrain the types of changes you can make.
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