Re: [Boost-users] Problem understanding 'boost::intrusive::list_member_hook<>'

11 Sep 2021

      On 11/09/2021 13:10, Joaquín M López Muñoz via Boost-users wrote:
...
...
Em 11 de set de 2021, à(s) 13:51, John Emmas via Boost-users 
 escreveu:
compiles now trigger a new assert in 'boost/intrusive/list.hpp':-
//Constant-time size is incompatible with auto-unlink hooks!
  BOOST_STATIC_ASSERT(!(constant_time_size &&
                       ((int)value_traits::link_mode == (int)auto_unlink)
                     ));
The comment above the assert says it all. Take a look at how 
constant_time_size<false> is used in the docs for auto-unlink hooks.
Thanks again Joaquin - AFAICT the only occurrences of 
'constant_time_size' are within libboost itself.  In fact for 'class 
list_impl' it seems to be defined as a constant:-

     static const bool constant_time_size = ConstantTimeSize;

However, I've realised that the problem I reported initially (today) 
does seem to be connected to DLL linkage somehow.  For example, this 
code in a source file compiles okay:-

     #include 
     class Point : public boost::intrusive::list_base_hook<> {
     };

whereas this seemingly minor change:-

     #include 
     class __declspec(dllexport) Point : public 
boost::intrusive::list_base_hook<> {
};

will immediately invoke this compile-time assertion:- 
"BOOST_STATIC_ASSERT(( (int)hooktags::link_mode == (int)auto_unlink ));" 
- i.e. the message I reported earlier...

So (presumably ?) 'boost::intrusive::list_base_hook<>' can't be used in 
a class that'll get exported from a DLL?

John