Re: [boost] [Review][bimap]

From: Thorsten Ottosen (thorsten.ottosen_at_[hidden])
Date: 2007-02-25 03:38:37

Matias Capeletto wrote:

 > On 2/24/07, Thorsten Ottosen <thorsten.ottosen_at_[hidden]> wrote:
 >
 >> Matias Capeletto wrote:
 >>
 >>> On 2/23/07, Thorsten Ottosen <thorsten.ottosen_at_[hidden]> wrote:
 >>
 >>
 >>>> Maybe I missed how one would use this view. How exactly (and which 
page
 >>>> in the documentation?)
 >>>
 >>>
 >>>
 >>> Maybe I have introduce noise here. The left view is the 
bidirectional mapping
 >>> view from the left, the one obtained with bm.left
 >>>
 >>> bimap<X,Y>::left_map_type is signature compatible with std::map<X,Y>.
 >>> bimap<X,Y>::left_map_type::value_type is signature-compatible with
 >>> std::pair<X,Y> and
 >>> bimap<X,Y>::right_map_type::value_type is signature-compatible with
 >>> std::pair<Y,X>
 >>>
 >>> So you can use this view or the right one with generic algorithms 
that need
 >>> first/second members.
 >>
 >>
 >> I missed that. It seems like there is less to worry about then :-)
 >
 >
 >
 >> Take this example:
 >>
 >>
 >>     typedef bimap<std::string,int> results_bimap;
 >>     typedef results_bimap::relation position;
 >>
 >>     results_bimap results;
 >>     results.insert( position("Argentina"    ,1) );
 >>     results.insert( position("Spain"        ,2) );
 >>     results.insert( position("Germany"      ,3) );
 >>     results.insert( position("France"       ,4) );
 >>
 >>
 >> I could not find any documentation on direct members of
 >> a bimap. Should it read results.left.insert()???
 >
 >
 >
 > No, there is some confusion here. The documentation will have to be
 > changed to help grasp the essence of bimap easier. Fernando Cacciola
 > has proposed some useful changes to the docs.

I looked in the reference section under bimap and it only stated 
constructors and types. Have I found some old documentation on the net 
somehow?

Anyway, I think I get it.

 >> std::make_pair() aside, you are often forced to
 >> constructing a pair object, only to copy its data once again upon
 >> insertion into the map.
 >
 >
 >
 > Can you give an example?

Well, the rvalue position objects created above is a good example:

1. creare rvalue string (non-trivial) and int (trivial) arguments

2. copy string and int in position constructor

3. upon insertion, copy string and int again

So the above takes

1 constructor call
2 copy-constructor calls

per argument, Removing 1 copy-constructor call is the goal here.

-Thorsten