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

Subject: Re: [boost] [Concepts] Definition. Was [GSoC] [Boost.Hana] Formal review request
From: Marc Glisse (marc.glisse_at_[hidden])
Date: 2014-08-14 02:25:49

On Wed, 13 Aug 2014, Robert Ramey wrote:

> It's true that compiler support for verification of all the type 
> requirements which someone might come up with falls short of perfection. 
> But as a practical matter, most type requirements are pretty simple and 
> easily supported with current type traits.  For example, type 
> requirements for
>
> template<class T>
> quick_sort(iterator<T> begin, iterator<T> end)
>
> are easily stated AND enforced:
> BOOST_CONCEPT_REQUIRES((Swappable<T>);
> BOOST_CONCEPT_REQUIRES((StrictWeakOrdering<T>));
>
> This is useful right now.  And few library authors even explicitly state
> their type requirements - much less include them in code.
>
> This could change in a month - and it will if I have anything to say
> about it.  There is absolutely no advantage to not doing this.

In general, yes, there is an advantage to not doing this: checking the 
requirements this way triggers some instantiations that you may need to 
delay. That's the main reason libstdc++ deprecated their concept checks 
(based on an early version of boost's), they broke too much code that 
ended up with cycles of A needs B needs C needs A.

-- 
Marc Glisse