Re: Problem understanding 'boost::intrusive::list_member_hook<>'

From: John Emmas (john_at_[hidden])
Date: 2021-09-09 09:28:12

On 08/09/2021 15:56, John Emmas wrote:
>
> I realise there are two types of hook available for 
> 'boost::intrusive::list' ( the list_member_hook<> and the 
> list_base_hook<>) - so are there certain situations where one would 
> preferable over the other?
>

Overnight I got told (off-list) that when 2 x classes are both declared 
using the 'list_base_hook<>' option, I'll get a runtime crash if I try 
to add the same object to both lists.  In other words, this will crash 
at the specified line:-

     class animal : public boost::intrusive::list_base_hook<>
     {
      public:
         animal (string n, int l) : name{move(n)}, legs{l} {}

         string name;
         int legs;
     };

     typedef boost::intrusive::list<animal> Animals;
     typedef boost::intrusive::list<animal> Dogs;

     int main()
     {
         animal a1{"labrador", 4};
         animal a2{"bulldog", 4};

         Animals animals;
         animals.push_back (a2);  // <--- 'bulldog' works okay

         Animals dogs;
         dogs.push_back (a1);     // <--- 'labrador' Works okay
         dogs.push_back (a2);     // <--- 'bulldog' crashes !!!

         return 0;
     }

and sure enough it does crash there!  So I then tried changing the 
design to use 'boost::intrusive::list_member_hook<>' but that gave me 
the same runtime crash... so is this just a general limitation with 
'boost::intrusive::list'?

Thanks again for any advice, John