Re: [boost] [hana] Lorenzo's Formal review for Hana

Subject: Re: [boost] [hana] Lorenzo's Formal review for Hana
From: Louis Dionne (ldionne.2_at_[hidden])
Date: 2015-06-27 10:27:30

> On 24 Jun 2015 at 22:07, Brian Wood wrote:
>
> > > Quite honestly, I'd rather have my library never get into Boost than
> > > bastardize it so it works on MSVC. If it can be made to work on MSVC
> > > without bastardizing it, however, I'm all for it.
>
> I think you have a good chance of getting it working on VS2017,
> though with some effort by you to do the port. Not bastardising it,
> but rather reformulating your code to work around lack of two phase
> lookup etc.

I'm OK with some effort, but I'm not OK with anything that involves a
significant amount of ugly workarounds. The last thing I want is for Hana
to fall into the same unmaintainability hell as the MPL is currently in
(for good reasons, no doubt).

BTW, just as a curiosity, why doesn't MSVC implement proper two-phase
lookup?

> I hope you're not using lambdas in template template parameters.
> Chandler tells me MSVC can't mangle some of those, and has to stop
> dead same as winclang has to.

Do you mean something like the following?

    auto lambda = []() { };
    tuple<decltype(lambda)> xs;

Off the top of my head, I don't think Hana uses this anywere.

> > I face similar issues and agree with your remarks here.  It seems
> > like it's easier to use MSVC and Windows than it used to be, but it's
> > still not easy.  I've recently reduced my Windows support and feel a
> > burden lifted.
>
> I have found VS2015 quite remarkably better than anything before. In
> developing my lightweight monad recently which involves plenty of
> hefty C++ 11 and 14 metaprogramming, I mainly used clang 3.6 on
> Linux, and then pushed changes to my Jenkins CI without any further
> local testing.
>
> Out of 100 builds, about four failed with GCC 5.1 due to GCC having
> incomplete/buggy constexpr support.
>
> Out of 100 builds, less than ten failed on VS2015 due to me using a
> construct it didn't like. Of course, I was deliberately avoiding
> Expression SFINAE etc, but the point is that VS2015 has enormously
> closed the gap with clang and GCC. Over 90% of the time in my case
> these last few weeks VS2015 will compile any C++ 11 or C++ 14 I wrote
> and tested only using clang on Linux. That's quite something compared
> to where we were only a year ago.

I'm glad to hear about this, I really am. I'm eager to see how their
support for modern C++ will evolve in the upcoming months/years. The
more compilers around for testing, the better.

Regards,
Louis

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