Re: [boost] Yap's formal review is starting now!

Subject: Re: [boost] Yap's formal review is starting now!
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2018-02-16 20:05:14

AMDG

On 02/16/2018 11:29 AM, Peter Dimov via Boost wrote:
> Steven Watanabe wrote:
> 
>> > As is, it isn't, because MSVC 2017 can't even include hana.hpp at >
>> present, let alone make any use of it.
>>
>> It took me about 5 minutes to fix that.
> 
> The implied argument being that it's better to fix Hana, or at least
> those parts of it that Yap uses, to compile under MSVC instead?
> 

  Yes.  After working around the decltype()::value problem, I
just had to add /permissive- to get (at least some of)
Hana's tests to build with msvc.  Yap itself has more
problems on msvc than Hana does.  (I gave up after seeing
it ICE in the SFINAE for tag transforms.)

> I still don't think it's better to have the user write
> 
> template <typename Expr1, typename Expr2, typename Expr3>
> decltype(auto) transform_expression (
> Â Â  boost::yap::expression<
> Â Â Â Â Â Â  boost::yap::expr_kind::plus,
> Â Â Â Â Â Â  boost::hana::tuple<
> Â Â Â Â Â Â Â Â Â Â  boost::yap::expression<
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â  boost::yap::expr_kind::multiplies,
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â  boost::hana::tuple<
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  Expr1,
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  Expr2
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â  >
> Â Â Â Â Â Â Â Â Â Â  >,
> Â Â Â Â Â Â Â Â Â Â  Expr3
> Â Â Â Â Â Â  >
> Â Â  > const & expr
> )
> 
> instead of
> 
> template <typename Expr1, typename Expr2, typename Expr3>
> decltype(auto) transform_expression (
> Â Â  boost::yap::expression<
> Â Â Â Â Â Â  boost::yap::expr_kind::plus,
> Â Â Â Â Â Â  std::tuple<
> Â Â Â Â Â Â Â Â Â Â  boost::yap::expression<
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â  boost::yap::expr_kind::multiplies,
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â  std::tuple<
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  Expr1,
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â Â  Expr2
> Â Â Â Â Â Â Â Â Â Â Â Â Â Â  >
> Â Â Â Â Â Â Â Â Â Â  >,
> Â Â Â Â Â Â Â Â Â Â  Expr3
> Â Â Â Â Â Â  >
> Â Â  > const & expr
> )
> 

Between these first two, I don't actually care.

> or
> 
> template <typename Expr1, typename Expr2, typename Expr3>
> decltype(auto) transform_expression (
> Â Â  boost::yap::expression<
> Â Â Â Â Â Â  boost::yap::expr_kind::plus,
> Â Â Â Â Â Â  boost::yap::expression<
> Â Â Â Â Â Â Â Â Â Â  boost::yap::expr_kind::multiplies,
> Â Â Â Â Â Â Â Â Â Â  Expr1,
> Â Â Â Â Â Â Â Â Â Â  Expr2
> Â Â Â Â Â Â  >,
> Â Â Â Â Â Â  Expr3
> Â Â  > const & expr
> )
> 

  This is a bit nicer in this case, but it's also a
bit of a trade-off as the requirements are more difficult
to state clearly.  Saying it must be exactly a
(hana|std)::tuple is completely unambiguous.  Also,
doing nested matching like this is somewhat imperfect
as it doesn't handle expr_refs transparently.

> but, whatever.
> 

In Christ,
Steven Watanabe