boost_1_45_0/libs/range/doc/style.qbk

[section:style_guide 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 );
``
 
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