Class sub_range

Класс<sub_range>наследует всю свою функциональность от класса<iterator_range>. Класс<sub_range>часто легче использовать, потому что нужно указатьпередний диапазон.Аргумент шаблона вместо итератора. Кроме того, класс<sub_range>может распространять константу, поскольку он знает, что такое соответствующая<const_iterator>.

Synopsis

namespace boost
{
    template< class ForwardRange >
    class sub_range : public iterator_range< typename range_iterator<ForwardRange>::type >
    {
    public:
        typedef typename range_value<ForwardRange>::type value_type;
        typedef typename range_iterator<ForwardRange>::type iterator;
        typedef typename range_iterator<const ForwardRange>::type  const_iterator;
        typedef typename range_difference<ForwardRange>::type difference_type;
        typedef typename range_size<ForwardRange>::type size_type;
        typedef typename range_reference<ForwardRange>::type reference;
        typedef typename range_reference<const ForwardRange>::type const_reference;
    public: // construction, assignment
        sub_range();
        template< class ForwardTraversalIterator >
        sub_range( ForwardTraversalIterator Begin, ForwardTraversalIterator End );
        template< class ForwardRange2 >
        sub_range( ForwardRange2& r );
        template< class ForwardRange2 >
        sub_range( const Range2& r );
        template< class ForwardRange2 >
        sub_range& operator=( ForwardRange2& r );
        template< class ForwardRange2 >
        sub_range& operator=( const ForwardRange2& r );
        // iterator accessors
        const_iterator begin() const;
        iterator begin();
        const_iterator end() const;
        iterator end();
        reference front();
        const_reference front() const;
        sub_range& advance_begin(difference_type n);
        sub_range& advance_end(difference_type n);
        // If traversal >= bidirectional:
        reference back();
        const_reference back();
        // If traversal >= random-access:
        reference operator[](difference_type n);
        const_reference operator[](difference_type n) const;
    public:
        // rest of interface inherited from iterator_range
    };
} // namespace 'boost'

The class should be trivial to use as seen below. Imagine that we have an algorithm that searches for a sub-string in a string. The result is an iterator_range, that delimits the match. We need to store the result from this algorithm. Here is an example of how we can do it with and without sub_range

std::string str("hello");
iterator_range<std::string::iterator> ir = find_first( str, "ll" );
sub_range<std::string>               sub = find_first( str, "ll" );