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

Subject: Re: [Boost-users] [intrusive] accessing the hook type?
From: Oliver Kowalke (oliver.kowalke_at_[hidden])
Date: 2015-10-18 14:00:02

2015-10-18 13:03 GMT+02:00 Ion Gaztañaga <igaztanaga_at_[hidden]>:

> 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
>

thx, using value_traits::hook_type helps

template< typename List >
void do_link( List & lst) {
    static_assert(std::is_same< typename List::value_traits::hook_type,
my_hook_type >::value);
    lst.push_back( * this);
}

best,
Oliver