Re: [Boost-users] boost::array < pair<>... > iterator adaptor

Subject: Re: [Boost-users] boost::array < pair<>... > iterator adaptor
From: Hicham Mouline (hicham_at_[hidden])
Date: 2009-04-02 11:30:49

>AMDG 
>Hicham Mouline wrote: 
>> I have a boost::array< pair<type1, type2>, maxsize > object, and I wish
to 
>> iterate over the list of type1 elements, and the list of type2
elements... 
>> 
>> I gather I then need an iterator adaptor based on array's iterator and 
>> const_iterators... 
>> How may I write such a thing? 
>> 
>> I then can pass around iterators to type1 and type2 separately. 
>> 
>transform_iterator might be useful. I don't know off 
>the top of my head whether there is a more specialized 
>iterator adaptor in Boost somewhere. 
Great, this worked beautifully

struct FirstElem : public std::unary_function< pair<>, double >
{
 double operator()( const pair<>& p )
 {
  return p.first;
 } 
};

typedef boost::transform_iterator< FirstElem, IterType >  FirstElemIterType;
FirstElemIterType feit ( container.begin() );

I can then pass feit around.

Now, under normal assumptions, accessing first elements through feit should
be as fast
as direct access by manual loop.... inline calls should be optimized away?

Thanks,