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1. Why is there no difference between range_iterator<C>::type and range_const_iterator<C>::type for std::pair<iterator, iterator>?

In general it is not possible nor desirable to find a corresponding const_iterator. When it is possible to come up with one, the client might choose to construct a std::pair<const_iterator,const_iterator> object.

Note that an iterator_range is somewhat more convenient than a pair and that a sub_range does propagate const-ness.

2. Why is there not supplied more types or more functions?

The library has been kept small because its current interface will serve most purposes. If and when a genuine need arises for more functionality, it can be implemented.

3. How should I implement generic algorithms for ranges?

One should always start with a generic algorithm that takes two iterators (or more) as input. Then use Boost.Range to build handier versions on top of the iterator based algorithm. Please notice that once the range version of the algorithm is done, it makes sense not to expose the iterator version in the public interface.

4. Why is there no Incrementable Range concept?

Even though we speak of incrementable iterators, it would not make much sense for ranges; for example, we cannot determine the size and emptiness of a range since we cannot even compare its iterators.

Note also that incrementable iterators are derived from output iterators and so there exist no output range.