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Subject: Re: [boost] Efficient tuple implementation
From: Niall Douglas (s_sourceforge_at_[hidden])
Date: 2014-06-08 10:34:30

On 7 Jun 2014 at 15:09, Louis Dionne wrote:

> > > Also, for those following the development of Boost.Hana, it is going
> > > well and I am preparing for a followup in the near future. Stay tuned!
> >
> > Louis, Microsoft have announced what's going to be in VS2015 at
> >
> > .aspx.
> I can't access this without signing up, but see below.

Eh, no it's definitely public. Check the link is correct, no spaces
etc. Failing that search google for Visual Studio "14" CTP.

> > I was wondering if Boost.Hana could work with VS2015? I mean, VS2014
> > will clearly be insufficient, but I'd like to know what you think
> > about VS2015. Note that VS2015 still will not have expression SFINAE
> > nor generalised constexpr nor template variables.
> Variable templates and generalized constexpr are used in the library.
> Workarounds _might_ be possible, but I have to say I'm unwilling to
> make the code less legible in favour of workarounds since Boost.Hana
> is a bleeding edge library.
> Still, if something can easily be done about it and make the library
> usable by massively more people, I will.

Well, you know the way you've been experimenting with alternative
ways of doing the same thing ...

I was thinking you could have a good Hana and a bad Hana :). Good
Hana is close to optimal for clang and GCC, while bad Hana is more
backwards compatible at the cost of pathological performance. You'd
obviously have preprocessor which switches the underlying
implementation depending on the compiler.

Do also bear in mind that MSVC is not an AST based compiler, so all
your benchmarks will look totally different on MSVC anyway. What may
have O(N^N) scaling on an AST compiler might well be O(N) on MSVC -
in fact, that is exactly why MSVC isn't AST based, as internal
Microsoft code is so complex it is uncompilable by an AST based
compiler. So if you are to support MSVC one day after C++ 14
conformance is reached, the techniques you currently optimise for may
well not be useful.

And MSVC isn't going anywhere. It's going to be a Tier 1 C++ compiler
for at least the next decade. This might help your design choices


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