Re: [Boost-users] [intrusive] accessing the hook type?

Subject: Re: [Boost-users] [intrusive] accessing the hook type?
From: Ion Gaztañaga (igaztanaga_at_[hidden])
Date: 2015-10-18 07:03:57

On 17/10/2015 18:04, Oliver Kowalke wrote:
> I'd like to determine the hook type of an intrusive container
> (intrusive::list):
>
> template< typename List >
> void do_link( List & lst) {
>     static_assert(std::is_same< typename List::???, my_hook_type >::value);
>     lst.push_back( * this);
> }

Hi,

There is no current typedef for that. The closest thing is 
"value_traits", which is what the container understands. Each hook type 
is transformed to "value_traits" which tells the container how the value 
and the node (stored in the hook) communicate.

If "value_traits" option is passed instead of a hook, then 
container::value_traits is the same type. If a hook is passed (or 
deduced, if the default hook is used), then that information is 
transformed in a "value_traits" defined here:

boost/intrusive/hook_traits.hpp

(e.g. boost::intrusive::detail::bhtraits<T, NodeTraits, LinkMode, Tag, 
Type> for a base hook).

If this information is important, then we should design a better 
interface to check it. "value_traits" is not a very good name for what 
it does, maybe "hook_traits" would have been a better name. The issue is 
that a "hook" (which could be deduced form "value_type" if the 
programmer does not provide it) is not directly transformed on what the 
container really uses ("value_traits").

Best,

Ion