Re: [boost] [interprocess][multi_index] emplace() is not sufficient for maps

Subject: Re: [boost] [interprocess][multi_index] emplace() is not sufficient for maps
From: Howard Hinnant (howard.hinnant_at_[hidden])
Date: 2009-09-24 10:27:18

On Sep 24, 2009, at 10:02 AM, Thorsten Ottosen wrote:

> Howard Hinnant skrev:
>> On Sep 19, 2009, at 4:18 AM, Thorsten Ottosen wrote:
>>> Ion Gaztañaga skrev:
>>>> Thorsten Ottosen escribió:
>
>> Suggestion:
>> Using std::map as an example as I am not familiar with  
>> [interprocess][multi_index].  Also using C++0X notation (to be  
>> emulated in C++03).
>> Add to the container:
>> template <class Key, class T, class Compare, class Allocator>
>> class map
>> {
>> public:
>>    ...
>>    typedef /details/ node_ptr;
>>    node_ptr remove(const_iterator p);
>>    pair<iterator, bool> insert(node_ptr&& nd);
>>    iterator             insert(const_iterator p, node_ptr&& nd);
>>    ...
>> };
>> map::node_ptr is a move-only smart pointer which holds an  
>> Allocator* and a map::node* (or equivalent smart pointer as  
>> interprocess may need?).  node_ptr roughly looks like:
>> template <class Key, class T, class Allocator>
>> class node_ptr
>> {
>>    node_ptr(const node_ptr&);
>>    node_ptr& operator=(const node_ptr&);
>> public:
>>    typedef pair<Key, T> value_type;
>>    node_ptr();
>>    ~node_ptr();
>>    node_ptr(node_ptr&& n);
>>    node_ptr& operator=(node_ptr&& n);
>>    void reset();
>>    value_type& operator*() const;
>>    value_type* operator->() const;
>> };
>
> I'm fine with this interface, and it seems less complicated compared  
> to Joaquin's modify_key().
>
> It doesn't quite address my first issue though, namely that I need  
> to construct the mapped value in the node, and then compute the key  
> from this mapped value (after some modification).
>
> I think if the node_ptr class had
>
> a) a forwarding (Key,Value) constructor
>
> b) an emplacing constructor that
> constructed the pair with (Key,...)
>
> then I could do exactly what I needed :-)

With what allocator would the node_ptr allocate the node?

-Howard