Re: [boost] [range] Problem with adaptors::map_keys

Subject: Re: [boost] [range] Problem with adaptors::map_keys
From: Alexander Fokin (apfokin_at_[hidden])
Date: 2010-11-29 02:44:24

> Three things:
> - value_type should just be pair< Key, T > (no reference or const
> qualifications on Key or T)
> - reference should be pair< Key const &, T& >, with T possibly
> const-qualified (as you've done)
> - you can (if you want) use iterator_adaptor instead of iterator_facade to
> automatically get a correct equal, increment, and decrement.
I have modified the code as you have suggested and now it compiles OK.
The modified code is available at http://codepad.org/AJFIVbdY.

However, there is one thing I'm concerned about. Consider the example
at http://codepad.org/plyTCBpx. The following lines do not call the
copy constructor of class A:
BOOST_FOREACH(auto pair, m) {
    const A &key = pair.first;
}

However, when I use range adaptors, the copy constructor is called.
That was exactly what I was trying to avoid by using references in
value_type.

I guess I'll try to fix this by myself and then file a patch.

-- 
Best regards,
  Alexander Fokin, http://elric.ru.