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

El 09/09/2021 a las 11:28, John Emmas via Boost-users escribió:

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<>     {        [...]     };

[...]

       animals.push_back (a2);  // <--- 'bulldog' works okay [...]        dogs.push_back (a2);     // <--- 'bulldog' crashes !!!

You're trying to insert a2 into dogs when the element is alredy inserted into animals. You can either remove a2 from animals beforehand:    animals.erase(Animals::s_iterator_to(a2)); or, if you mean for the elements to be allowed in both lists at the same time, use tags:     #include     #include <string>     #include <utility>     typedef boost::intrusive::list_base_hook animals_hook;     typedef boost::intrusive::list_base_hook dogs_hook;     class animal :       public animals_hook, public dogs_hook     {      public:         animal (std::string n, int l) : name{std::move(n)}, legs{l} {}         std::string name;         int legs;     };     typedef boost::intrusive::list> Animals;     typedef boost::intrusive::list> Dogs;     int main()     {         animal a1{"labrador", 4};         animal a2{"bulldog", 4};         Animals animals;         animals.push_back (a2);  // <--- 'bulldog' works okay         Dogs dogs;         dogs.push_back (a1);     // <--- 'labrador' works okay         dogs.push_back (a2);     // <--- 'bulldog' works okay         return 0;     } Joaquín M López Muñoz