indexed

indexed example

Syntax	Code
Pipe	`rng \| boost::adaptors::indexed()`
Pipe	`rng \| boost::adaptors::indexed(start_index)`
Function	`boost::adaptors::index(rng)`
Function	`boost::adaptors::index(rng, start_index)`

The index within each returned boost::range::index_value is equal to start_index + the offset of the element from the beginning of the range. In the versions of the functions that omit start_index the starting index is taken to be 0.

Purpose: Adapt rng to return elements that have the corresponding value from rng and a numeric index.
Returns: A range adapted to return both the element and the associated index. The returned range has elements of type:

boost::range::index_value<
    typename boost::range_reference<decltype(rng)>::type,
    typename boost::range_difference<decltype(rng)>::type
>

The synopsis of index_value is as follows:

template<class T, class Indexable=std::ptrdiff_t>
class index_value : public boost::tuple<Indexable, T>
{
public:

    typedef ...unspecified...       index_type;
    typedef ...unspecified...       const_index_type;

    typedef ...unspecified...       value_type;
    typedef ...unspecified...       const_value_type;

    // ...unspecified... constructors

    index_type index();
    const_index_type index() const;

    value_type value();
    const_value_type value() const;
};

Range Category: Single Pass Range
Range Return Type: boost::indexed_range<decltype(rng)>
Returned Range Category: The range category of rng if and only if rng is not a Bidirectional Range. If rng is a Bidirectional Range then the returned range category is Forward Range. The rationale for the demotion of Bidirectional Range inputs to Forward Range is to avoid slow calculation of indices for boost::end(rng).

indexed example

#include <boost/range/adaptor/indexed.hpp>
#include <boost/assign.hpp>
#include <iterator>
#include <iostream>
#include <vector>


int main(int argc, const char* argv[])
{
    using namespace boost::assign;
    using namespace boost::adaptors;

    std::vector<int> input;
    input += 10,20,30,40,50,60,70,80,90;

    for (const auto& element : input | indexed(0))
    {
        std::cout << "Element = " << element.value()
                  << " Index = " << element.index()
                  << std::endl;
    }

    return 0;
}

This would produce the output:

Element = 10 Index = 0
Element = 20 Index = 1
Element = 30 Index = 2
Element = 40 Index = 3
Element = 50 Index = 4
Element = 60 Index = 5
Element = 70 Index = 6
Element = 80 Index = 7
Element = 90 Index = 8

indexed

Description

indexed example