Boost.Range Reference

| # Boost.Range

## Synopsis and Reference

- Overview
- Synopsis
- Semantics
- Extending the library

### Overview

Four types of objects are currently supported by the library:

- standard-like containers
- `std::pair<iterator,iterator>`
- null terminated strings (this includes `char[]`,`wchar_t[]`, `char*`, and `wchar_t*`)

  Warning: support for null-terminated strings is deprecated and will disappear in the next Boost release (1.34).

- built-in arrays

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_value;

        template< class T >
        struct range_iterator;

        template< class T >
        struct range_const_iterator;

        //
        // Forward Range metafunctions
        //

        template< class T >
        struct range_difference;

        template< class T >
        struct range_size;

        //
        // Bidirectional Range metafunctions
        //

        template< class T >
        struct range_reverse_iterator;

        template< class T >
        struct range_const_reverse_iterator;

        //
        // Special metafunctions
        //

        template< class T >
        struct range_result_iterator;

        template< class T >
        struct range_reverse_result_iterator;

        //
        // Single Pass Range functions
        //

        template< class T >
        typename range_iterator<T>::type
        begin( T& c );

        template< class T >
        typename range_const_iterator<T>::type
        begin( const T& c );

        template< class T >
        typename range_iterator<T>::type
        end( T& c );

        template< class T >
        typename range_const_iterator<T>::type
        end( const T& c );

        template< class T >
        bool
        empty( const T& c );

        //
        // Forward Range functions
        //

        template< class T >
        typename range_size<T>::type
        size( const T& c );

        //
        // Bidirectional Range functions
        //

        template< class T >
        typename range_reverse_iterator<T>::type
        rbegin( T& c );

        template< class T >
        typename range_const_reverse_iterator<T>::type
        rbegin( const T& c );

        template< class T >
        typename range_reverse_iterator<T>::type
        rend( T& c );

        template< class T >
        typename range_const_reverse_iterator<T>::type
        rend( const T& c );

        //
        // Special const Range functions
        //

        template< class T >
        typename range_const_iterator<T>::type
        const_begin( const T& r );

        template< class T >
        typename range_const_iterator<T>::type
        const_end( const T& r );

        template< class T >
        typename range_const_reverse_iterator<T>::type
        const_rbegin( const T& r );

        template< class T >
        typename range_const_reverse_iterator<T>::type
        const_rend( 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_value<X>::type` | `T::value_type` `boost::iterator_value<P::first_type>::type` `A` `Char` | compile time
`range_iterator<X>::type` | `T::iterator` `P::first_type` `A*` `Char*` | compile time
`range_const_iterator<X>::type` | `T::const_iterator` `P::first_type` `const A*` `const Char*` | compile time
`range_difference<X>::type` | `T::difference_type` `boost::iterator_difference<P::first_type>::type` `std::ptrdiff_t` `std::ptrdiff_t` | compile time
`range_size<X>::type` | `T::size_type` `std::size_t` `std::size_t` `std::size_t` | compile time
`range_result_iterator<X>::type` | `range_const_iterator<X>::type` if `X` is `const` `range_iterator<X>::type` otherwise | compile time
`range_reverse_iterator<X>::type` | `boost::reverse_iterator< typename range_iterator<T>::type >` | compile time
`range_const_reverse_iterator<X>::type` | `boost::reverse_iterator< typename range_const_iterator<T>::type >` | compile time
`range_reverse_result_iterator<X>::type` | `boost::reverse_iterator< typename range_result_iterator<T>::type >` | compile time

The special metafunctions `range_result_iterator` and `range_reverse_result_iterator` are not part of any Range concept, but they are very useful when implementing certain Range classes like `sub_range` because of their ability to select iterators based on constness.

#### Functions

Expression | Return type | Returns | Complexity
--- | --- | --- | ---
`begin(x)` | `range_result_iterator<X>::type` | `p.first` if `p` is of type `std::pair<T>``a` if `a` is an array `s` if `s` is a string literal `boost_range_begin(x)` if that expression would invoke a function found by ADL `t.begin()` otherwise`` | constant time
`end(x)` | `range_result_iterator<X>::type` | `p.second` if `p` is of type `std::pair<T>``a + sz` if `a` is an array of size `sz` `s + std::char_traits<X>::length( s )` if `s` is a `Char*` `s + sz - 1` if `s` is a string literal of size `sz` `boost_range_end(x)` if that expression would invoke a function found by ADL `t.end()` otherwise`` | linear if `X` is `Char*` constant time otherwise
`empty(x)` | `bool` | `begin(x) == end( x )` | linear if `X` is `Char*` constant time otherwise
`size(x)` | `range_size<X>::type` | `std::distance(p.first,p.second)` if `p` is of type `std::pair<T>``sz` if `a` is an array of size `sz` `end(s) - s` if `s` is a string literal or a `Char*` `boost_range_size(x)` if that expression would invoke a function found by ADL `t.size()` otherwise`` | linear if `X` is `Char*` or if `std::distance()` is linear constant time otherwise
`rbegin(x)` | `range_reverse_result_iterator<X>::type` | `range_reverse_result_iterator<X>::type( end(x) )` | same as `end(x)`
`rend(x)` | `range_reverse_result_iterator<X>::type` | `range_reverse_result_iterator<X>::type( begin(x) )` | same as `begin(x)`
`const_begin(x)` | `range_const_iterator<X>::type` | `range_const_iterator<X>::type( begin(x) )` | same as `begin(x)`
`const_end(x)` | `range_const_iterator<X>::type` | `range_const_iterator<X>::type( end(x) )` | same as `end(x)`
`const_rbegin(x)` | `range_const_reverse_iterator<X>::type` | `range_const_reverse_iterator<X>::type( rbegin(x) )` | same as `rbegin(x)`
`const_rend(x)` | `range_const_reverse_iterator<X>::type` | `range_const_reverse_iterator<X>::type( rend(x) )` | same as `rend(x)`

The special `const` functions are not part of any Range concept, but are very useful when you want to document clearly that your code is read-only.

### Extending the library

- Method 1: provide member functions and nested types
- Method 2: provide free-standing functions and specialize metafunctions

#### 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
`size()` | Forward 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
`size_type` | Forward 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
--- | ---
`boost_range_begin(x)` | Single Pass Range
`boost_range_end(x)` | Single Pass Range
`boost_range_size(x)` | Forward Range

`boost_range_begin()` and `boost_range_end()` must be overloaded for both `const` and mutable reference arguments.

You must also specialize 3 metafunctions for your type `X`:

Metafunction | Related concept
--- | ---
`boost::range_iterator` | Single Pass Range
`boost::range_const_iterator` | Single Pass Range
`boost::range_size` | Forward 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_iterator< Foo::Pair<T> >
>     	{
>     		typedef T type;
>     	};

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

>     	template< class T >
>     	struct range_size< Foo::Pair<T> >
>     	{

>     		typedef std::size_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 boost_range_begin( Pair<T>& x )
>     	{
>     		return x.first;
>     	}

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

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

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

>     	template< class T >
>     	inline typename boost::range_size< Pair<T> >::type
>     	boost_range_size( const Pair<T>& x )
>     	{
>     		return std::distance(x.first,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_size< Foo::Pair<iter> >::type s = boost::size( pair );
>     	s      = boost::size( cpair );
>     	boost::range_const_reverse_iterator< Foo::Pair<iter> >::type
>     	ri     = boost::rbegin( cpair ),
>     	re     = boost::rend( cpair );
>     }

(C) Copyright Thorsten Ottosen 2003-2004