Re: [boost] [Iterator] Adaptors for accessing keys/values in associative containers

From: Giovanni Piero Deretta (gpderetta_at_[hidden])
Date: 2007-08-09 16:10:13

On 8/9/07, Joseph Gauterin <joseph.gauterin_at_[hidden]> wrote:
> Would anyone be interested in having a couple of extra specialized
> iterator adaptors in  Boost.Iterator?
>
> I'm thinking of 'key_iterator' and 'value_iterator' adaptors (along
> with convenience 'make_key_iterator' and 'make_value_iterator'
> functions) that allow any associative container (that follows standard
> library idioms) to be accessed as either a range of keys or as a range
> of values.
>

These would add very little that what transform_iterator already does.
What would be more
useful would be two function objects called first and second to access
the first or the second element of a pair.

Also function object wrappers for boost.tuple get<N> would really be useful.

In addition to transform_iterator, they would be very useful in bind
and boost.lambda
expressions.

BTW, I think that boost.bimap already provides them.

> They'd be used like this:
>
> std::map<std::string,int> m;
> std::for_each(make_value_iterator(m.begin()),make_value_iterator(m.end()),func);
>

With the above functors, you would spell that

std::for_each(
   make_transform_iterator(m.begin(), second()),
   make_transform_iterator(m.end(), second())),func);

At this point, is it really worth to have separate key/value_iterators?

gpd