Re: [boost] boost equivalents for select1st and select2nd

From: Michael Goldshteyn (mgoldshteyn_at_[hidden])
Date: 2006-01-31 12:44:30

"Marcin Kalicinski" <kalita_at_[hidden]> wrote in message 
news:drmai0$4k0$1_at_sea.gmane.org...
>> MyMap mymap; // A map of some key type to some value type
>> MyVector myvector; // A vector of elements either of key type or value
>
> (...)
>
>> // Implementation using boost::bind
>> transform(mymap.begin(),mymap.end(),back_inserter
>>(myvector),boost::bind(&MyMap::value_type::second,_1));
>
> And here's the most straighforward of them, but overlooked, implementation 
> using BOOST_FOREACH, no std-omitting was necessary at all:
>
> BOOST_FOREACH(const MyMap::value_type &v, mymap)
>    myvector.push_back(v.first);
>
> cheers,
> Marcin

An interesting alternate solution, but I was mainly looking for a way that 
didn't involve directly using a for loop or a derivative thereof in my code. 
That is to say, I was trying to just use a standard algorithm (i.e. 
transform), rather than coding a loop, which despite appearances is what 
BOOST_FOREACH is. Note that I am not arguing which way is better, only 
presenting a solution to those who like for_each and transform.

I have to say, though, that BOOST_FOREACH does have its uses and certainly 
allows for a more concise and less error prone way to do something with each 
object in a container.

The best solution to the problem is to have standard copy_keys and 
copy_values algorithms which, similar to transform takes begin and end 
iterators to the source and destination ranges, performing the necessary 
.first/.second accesses and then just a straight copy. In fact, I think this 
whole ordeal has inspired me enough to perhaps add these to the boost wiki 
site.

Michael Goldshteyn