Re: [boost] [GSoC] [Boost.Hana] Formal review request

Subject: Re: [boost] [GSoC] [Boost.Hana] Formal review request
From: pfultz2 (pfultz2_at_[hidden])
Date: 2014-08-01 06:55:12

> I'm a bit worried that:
> - Hana exposes a C++1y library-based implementation of concepts on its
> interface (typeclasses). Would moving it to concepts (once we get
> language-support in 2015/16) introduce a big breaking change?

Concepts are not being added in the near future to C++. Concepts lite is
proposed to add concept predicates to C++, which is very different.

> Then, Range-v3, TICK, Hana, and others are all using _different_ C++11/1y
> library-based implementations of concept checking which I guess means
> that:
> - there is need for such a library, and
> - Boost.ConceptCheck is for whatever reason not good enough in C++11/1y
> world yet. 

Hana does implement a form of concepts in C++. The Tick library only
implements
a form of concept predicates, which was based on what is done in the
Range-V3.
Of course, it might make sense to make Hana's typeclass a separate
library(although it should be called 'concepts' instead).

Of course, Boost.ConceptCheck is only good for improving error messages. It
is
very inadequate, and can be very problematic when combined with concept
predicates.

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