[boost] Re: Collection concept

From: John Maddock (John_Maddock_at_[hidden])
Date: 2000-01-16 07:39:16

Howard,

>Probably (I wasn't there when iter_swap was introduced).  But if 
>iter_swap is implemented like:
>
>template <class ForwardIterator1, class ForwardIterator2>
>void
>iter_swap(ForwardIterator1 a, ForwardIterator2 b)
>{
>       typedef typename iterator_traits<ForwardIterator1>::value_type 
>value_type;
>       value_type tmp(*a);
>       *a = *b;
>       *b = tmp;
>}
>
>the performance is poor for heavy value_types that have otherwise 
>specialized swap.  But it does (usually) work with proxied references.
>

You missed a chance to push type_traits here :-)

By using "is_reference<typename
iterator_traits<ForwardIterator1>::reference>::value", iter_swap can
seemlessly switch between the "slow and safe" proxy iterator approach, and
calling swap (which is more likely to be specialised IMO), see the type
traits examples.

- John