Re: [boost] Does Boost has an utility to replace all OLD Keys with NEW one for MultiMap/Map?

Subject: Re: [boost] Does Boost has an utility to replace all OLD Keys with NEW one for MultiMap/Map?
From: Tushar Chowdhury (tchowdhury80_at_[hidden])
Date: 2009-05-08 10:27:44

On Thu, May 7, 2009 at 2:05 PM, Duncan Smith
<duncanphilipnorman_at_[hidden]>wrote:

> 2009/5/7 Phil Endecott <spam_from_boost_dev_at_[hidden]>
> > template <typename CONT>
> > void replace_key(CONT& cont, typename CONT::key_type oldk, typenamme
> CONT::key_type newk)
> > {
> >  if (newk==oldk) return;
> >
> >  typedef typename CONT::iterator iter;
> >  std::pair<iter,iter> r = cont::equal_range(oldk);
> >  iter hint = cont.begin();
> >  for (iter i = r.first; i != r.second; ++r) {
> >    hint = cont.insert(hint,std::make_pair(newk,i->second));
> >  }
> >  cont.erase(r.first,r.second);
> > }
> As Phil mentioned, the range returned from 'equal_range()'  will
> expand when you do 'cont.insert()' if the oldk < newk < (the next key
> larger than oldk), causing an infinite loop during insertion.  Then,
> both sets of keys will get erased with 'erase()'.
>
> The easiest way to do this robustly is with temporary storage:
>
> #include <algorithm>
> #include <boost/bind.hpp>
> #include <boost/ref.hpp>
> #include <utility>
> #include <vector>
>
> template <typename Container>
> void replace_key(Container &c, typename Container::key_type oldKey,
> typename Container::key_type newKey)
> {
>  if (oldKey != newKey) {
>    typedef typename Container::iterator iterator;
>    typedef typename Container::value_type value_type;
>    typedef typename Container::key_type key_type;
>    typedef typename Container::mapped_type mapped_type;
>    using ::std::make_pair;
>    using ::std::vector;
>    using ::boost::bind;
>    using ::boost::cref;
>    using ::std::transform;
>
>    std::pair<iterator, iterator> range = c.equal_range(oldKey);
>    std::vector<mapped_type> values;
>    transform(range.first, range.second,
>      std::back_inserter(values),
>      bind(&value_type::second, _1));
>
>    c.erase(range.first, range.second);
>
>    transform(values.begin(), values.end(),
>      std::inserter(c, c.end()),
>      bind(make_pair<key_type, mapped_type>, cref(newKey), _1));
>  }
> }
>
> There are more efficient implementations, but this should do it.
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