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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
a form of concept predicates, which was based on what is done in the
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
very inadequate, and can be very problematic when combined with concept

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