| # Boost.Range

## Terminology and style guidelines

The use of a consistent terminology is as important for Ranges and range-based algorithms as it is for iterators and iterator-based algorithms. If a conventional set of names are adopted, we can avoid misunderstandings and write generic function prototypes that are self-documenting.

Since ranges are characterized by a specific underlying iterator type, we get a type of range for each type of iterator. Hence we can speak of the following types of ranges:

- Value access category:
  - Readable Range
  - Writeable Range
  - Swappable Range
  - Lvalue Range
- Traversal category:
  - Single Pass Range
  - Forward Range
  - Bidirectional Range
  - Random Access Range

Notice how we have used the categories from the new style iterators.

Notice that an iterator (and therefore an range) has one traversal property and one or more properties from the value access category. So in reality we will mostly talk about mixtures such as

- Random Access Readable Writeable Range
- Forward Lvalue Range

By convention, we should always specify the traversal property first as done above. This seems reasonable since there will only be one traversal property, but perhaps many value access properties.

It might, however, be reasonable to specify only one category if the other category does not matter. For example, the iterator_range can be constructed from a Forward Range. This means that we do not care about what value access properties the Range has. Similarly, a Readable Range will be one that has the lowest possible traversal property (Single Pass).

As another example, consider how we specify the interface of `std::sort()`. Algorithms are usually more cumbersome to specify the interface of since both traversal and value access properties must be exactly defined. The iterator-based version looks like this:

       template< class RandomAccessTraversalReadableWritableIterator >
       void sort( RandomAccessTraversalReadableWritableIterator first,
                  RandomAccessTraversalReadableWritableIterator last );

For ranges the interface becomes

       template< class RandomAccessReadableWritableRange >
       void sort( RandomAccessReadableWritableRange& r );

© Copyright Thorsten Ottosen 2008.

Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at www.boost.org/LICENSE_1_0.txt)