Boost.Range

Synopsis and Reference

Overview

Three types of objects are currently supported by the library:

Even though the behavior of the primary templates are exactly such that standard containers will be supported by default, the requirements are much lower than the standard container requirements. For example, the utility class iterator_range implements the minimal interface required to make the class a Forward Range .

Please also see Range concepts for more details.

Synopsis

namespace boost
{
    //
    // Single Pass Range metafunctions
    //
                   
    template< class T >
    struct range_iterator;
    
    template< class T >
    struct range_value;
  
    template< class T >
    struct range_reference;

    template< class T >
    struct range_pointer;
    
    template< class T >
    struct range_category;

    //
    // Forward Range metafunctions
    //
    
    template< class T >
    struct range_difference;
    
    //
    // Bidirectional Range metafunctions
    //
    
    template< class T >
    struct range_reverse_iterator;
    
    //
    // Single Pass Range functions
    //
    
    template< class T >
    typename range_iterator<T>::type
    begin( T& r );
    
    template< class T >
    typename range_iterator<const T>::type
    begin( const T& r );
        
    template< class T >
    typename range_iterator<T>::type
    end( T& r );
                      
    template< class T >
    typename range_iterator<const T>::type
    end( const T& r );
    
    template< class T >
    bool
    empty( const T& r );
               
    //
    // Forward Range functions
    //
    
    template< class T >
    typename range_difference<T>::type
    distance( const T& r );
                            
    //
    // Bidirectional Range functions
    //
                     
    template< class T >
    typename range_reverse_iterator<T>::type
    rbegin( T& r );
    
    template< class T >
    typename range_reverse_iterator<const T>::type
    rbegin( const T& r );
        
    template< class T >
    typename range_reverse_iterator<T>::type
    rend( T& r );
                      
    template< class T >
    typename range_reverse_iterator<const T>::type
    rend( const T& r );
    
    //
    // Random Access Range functions
    //
    
    template< class T >
    typename range_difference<T>::type
    size( const T& r );
    
    //
    // Special const Range functions
    // 
    
    template< class T >
    typename range_iterator<const T>::type 
    const_begin( const T& r );
    
    template< class T >
    typename range_iterator<const T>::type 
    const_end( const T& r );
    
    template< class T >
    typename range_reverse_iterator<const T>::type 
    const_rbegin( const T& r );
    
    template< class T >
    typename range_reverse_iterator<const T>::type 
    const_rend( const T& r );

    //
    // String utilities
    //
    
    template< class T >
    iterator_range<...see below...> 
    as_literal( T& r );

    template< class T >
    iterator_range<...see below...> 
    as_literal( const T& r );

    template< class T >
    iterator_range< typename range_iterator<T>::type > 
    as_array( T& r );

    template< class T >
    iterator_range< typename range_iterator<const T>::type > 
    as_array( const T& r );

} // namespace 'boost'

Semantics

notation

Type Object Describes
X x any type
T t denotes behavior of the primary templates
P p denotes std::pair<iterator,iterator>
A[sz] a denotes an array of type A of size sz
Char* s denotes either char* or wchar_t*

Please notice in tables below that when four lines appear in a cell, the first line will describe the primary template, the second line pairs of iterators, the third line arrays and the last line null-terminated strings.

Metafunctions

Expression Return type Complexity
range_iterator<X>::type T::iterator
P::first_type
A*
compile time
range_iterator<const X>::type T::const_iterator
P::first_type
const A*
compile time
range_value<X>::type boost::iterator_value<range_iterator<X>::type>::type compile time
range_reference<X>::type boost::iterator_reference<range_iterator<X>::type>::type compile time
range_pointer<X>::type boost::iterator_pointer<range_iterator<X>::type>::type compile time
range_category<X>::type boost::iterator_category<range_iterator<X>::type>::type compile time
range_difference<X>::type boost::iterator_difference<range_iterator<X>::type>::type compile time
range_reverse_iterator<X>::type boost::reverse_iterator<range_iterator<X>::type>
compile time
range_reverse_iterator<const X>::type boost::reverse_iterator<range_iterator<const X>::type>
compile time

Functions

Expression Return type Returns Complexity
begin(x) range_iterator<X>::type p.first if p is of type std::pair<T>
a if a is an array
range_begin(x) if that expression would invoke a function found by ADL
t.begin() otherwise 		constant time
end(x) range_iterator<X>::type p.second if p is of type std::pair<T>
a + sz if a is an array of size sz
range_end(x) if that expression would invoke a function found by ADL
t.end() otherwise 		constant time
empty(x) bool boost::begin(x) == boost::end(x)
 constant time
distance(x) range_difference<X>::type std::distance(boost::begin(x),boost::end(x)) -
size(x) range_difference<X>::type boost::end(x) - boost::begin(x) constant time
rbegin(x) range_reverse_iterator<X>::type range_reverse_iterator<X>::type( boost::end(x) )
constant time
rend(x) range_reverse_iterator<X>::type range_reverse_iterator<X>::type( boost::begin(x) ) constant time
const_begin(x) range_iterator<const X>::type range_iterator<const X>::type( boost::begin(x) )
constant time
const_end(x) range_iterator<const X>::type range_iterator<const X>::type( boost::end(x) ) constant time
const_rbegin(x) range_reverse_iterator<const X>::type range_reverse_iterator<const X>::type( boost::rbegin(x) )
constant time
const_rend(x) range_reverse_iterator<const X>::type range_reverse_iterator<const X>::type( boost::rend(x) ) constant time
as_literal(x) iterator_range<U> where U is Char* if x is a pointer to a string and U is range_iterator<X>::type otherwise [s,s + std::char_traits<X>::length(s)) if s is a Char* or an array of Char
[boost::begin(x),boost::end(x)) otherwise 		linear time for pointers to a string or arrays of Char, constant time otherwise
as_array(x) iterator_range<X> [boost::begin(x),boost::end(x)) constant time otherwise

The special const_-named functions are useful when you want to document clearly that your code is read-only.

as_literal() can be used internally in string algorithm librararies such that arrays of characters are handled correctly.

as_array() can be used with string algorithm libraries to make it clear that arrays of characters are handled like an array and not like a string.

Notice that the above functions should always be called with qualification (boost::) to prevent unintended Argument Dependent Lookup (ADL).

Extending the library

Method 1: provide member functions and nested types

This procedure assumes that you have control over the types that should be made conformant to a Range concept. If not, see method 2.

The primary templates in this library are implemented such that standard containers will work automatically and so will boost::array. Below is given an overview of which member functions and member types a class must specify to be useable as a certain Range concept.

Member function Related concept
begin() Single Pass Range
end() Single Pass Range

Notice that rbegin() and rend() member functions are not needed even though the container can support bidirectional iteration.

The required member types are:

Member type Related concept
iterator Single Pass Range
const_iterator Single Pass Range

Again one should notice that member types reverse_iterator and const_reverse_iterator are not needed.

Method 2: provide free-standing functions and specialize metafunctions

This procedure assumes that you cannot (or do not wish to) change the types that should be made conformant to a Range concept. If this is not true, see method 1.

The primary templates in this library are implemented such that certain functions are found via argument-dependent-lookup (ADL). Below is given an overview of which free-standing functions a class must specify to be useable as a certain Range concept. Let x be a variable (const or mutable) of the class in question.

Function Related concept
range_begin(x) Single Pass Range
range_end(x) Single Pass Range

range_begin() and range_end() must be overloaded for both const and mutable reference arguments.

You must also specialize two metafunctions for your type X:

Metafunction Related concept
boost::range_mutable_iterator Single Pass Range
boost::range_const_iterator Single Pass Range

A complete example is given here: 

#include <boost/range.hpp>
#include <iterator>         // for std::iterator_traits, std::distance()

namespace Foo
{
    //
    // Our sample UDT. A 'Pair'
    // will work as a range when the stored
    // elements are iterators.
    //
    template< class T >
    struct Pair
    {
        T first, last;  
    };

} // namespace 'Foo'

namespace boost
{
    //
    // Specialize metafunctions. We must include the range.hpp header.
    // We must open the 'boost' namespace.
    //

    template< class T >
    struct range_mutable_iterator< Foo::Pair<T> >
    {
        typedef T type;
    };

    template< class T >
    struct range_const_iterator< Foo::Pair<T> >
    {
        //
        // Remark: this is defined similar to 'range_mutable_iterator'
        //         because the 'Pair' type does not distinguish
        //         between an iterator and a const_iterator.
        //
        typedef T type;
    };

} // namespace 'boost'

namespace Foo
{
    //
    // The required functions. These should be defined in
    // the same namespace as 'Pair', in this case 
    // in namespace 'Foo'.
    //
    
    template< class T >
    inline T range_begin( Pair<T>& x )
    { 
        return x.first;
    }

    template< class T >
    inline T range_begin( const Pair<T>& x )
    { 
        return x.first;
    }

    template< class T >
    inline T range_end( Pair<T>& x )
    { 
        return x.last;
    }

    template< class T >
    inline T range_end( const Pair<T>& x )
    { 
        return x.last;
    }

} // namespace 'Foo'

#include <vector>

int main()
{
    typedef std::vector<int>::iterator  iter;
    std::vector<int>                    vec;
    Foo::Pair<iter>                     pair  = { vec.begin(), vec.end() };
    const Foo::Pair<iter>&              cpair = pair; 
    //
    // Notice that we call 'begin' etc with qualification. 
    //
    iter i = boost::begin( pair );
    iter e = boost::end( pair );
    i      = boost::begin( cpair );
    e      = boost::end( cpair );
    boost::range_difference< Foo::Pair<iter> >::type s = boost::size( pair );
    s      = boost::size( cpair );
    boost::range_reverse_iterator< const Foo::Pair<iter> >::type
    ri     = boost::rbegin( cpair ),
    re     = boost::rend( cpair );
}

© 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)