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

Subject: Re: [boost] [interprocess][multi_index] emplace() is not sufficient for maps
From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2009-09-18 15:41:42

Thorsten Ottosen skrev:
> Hi Ion and Joaquín,
> 
> This issue is related to node-based containers. I think you both have 
> added emplace() to provide efficient in-place construction.
> 
> However, I often encounter a situation where emplace() is not sufficient 
> for me.

I actually got into a situation where I need another member function.
The issue arises when I use map/set as a priority_queue and want to
limit the size of the queue. In this situation I will be erasing one 
element and inserting one element again and again. Unless the map/set
keeps a free-list of previously erased elements (which I don't think 
they do normally) we will be deallocating and allocating a new node over 
and over again.

Therefore I would like to see the follwing member:

   iterator modify_key( const_iterator element, const Key& new_key );

This function only needs to rebalance/resort the keys and can completely 
avoid deallocation/allocation.

Thoughts?

-Thorsten