Re: [boost] A proposal for the creation of a new module, Core Type Traits

Subject: Re: [boost] A proposal for the creation of a new module, Core Type Traits
From: Peter Dimov (lists_at_[hidden])
Date: 2015-01-08 09:04:42

John Maddock wrote:
> > These two problems could be avoided if we were to have core type traits 
> > whose interface consisted solely of a member integral constant called 
> > "value", without any other required members or base classes, and which 
> > were only allowed to depend on Config or StaticAssert.
>
> I'm less keen on this because it fractures the lib into two conceptually 
> different parts.  Let me mess around with some code and see if something 
> better is possible.

As I tried to explain further down, it simply separates the two already 
existing layers in the library: the part that computes the value of the 
trait, which results in something like is_pointer_impl<T>::value, and the 
part that defines the trait, which is generally implemented like this:

BOOST_TT_AUX_BOOL_TRAIT_DEF1(is_pointer,T,::boost::detail::is_pointer_impl<T>::value)

This separation is natural, in that the library already does it.

You're right that some traits will not be able to fit into the core part, 
most obviously common_type. But the users of the core part generally do not 
need them; and for those who do, well, they'll have to bite the bullet and 
use TypeTraits.

Or perhaps I'm missing your point?