Re: [Boost-users] units and existing APIs

Subject: Re: [Boost-users] units and existing APIs
From: Steven Watanabe (watanabesj_at_[hidden])
Date: 2008-11-03 16:17:52

AMDG

Joseph Winston III wrote:
> I would like to use boost::units in a new application that must 
> interface to existing APIs that do not provide templated interfaces.  
> What is the easiest way to use these existing functions that minimizes 
> the copying of data from raw C pointers to a container that holds a 
> specific type of boost::units?

Would a view like this be helpful?

#include <boost/iterator/transform_iterator.hpp>
#include <boost/units/quantity.hpp>
#include <boost/units/systems/si.hpp>
#include <iostream>
#include <algorithm>

using namespace boost::units;

template<class T>
class quantity_view {
    struct wrap_in_quantity {
        typedef T result_type;
        result_type operator()(const typename T::value_type& arg) const {
            return(T::from_value(arg));
        }
    };
public:
    typedef typename T::value_type storage_value_type;
    typedef T value_type;
    typedef boost::transform_iterator<
        wrap_in_quantity,
        const storage_value_type*> iterator;
    typedef iterator const_iterator;
    quantity_view(const storage_value_type* impl, std::size_t size)
        : impl(impl), size(size) {}
    const_iterator begin() const {
        return(iterator(impl));
    }
    const_iterator end() const {
        return(iterator(impl + size));
    }
private:
    const storage_value_type* impl;
    std::size_t size;
};

int main() {
    double data[] = {1, 2, 3, 4, 5};
    quantity_view<quantity<si::time> > tester(&data[0], 5);
    std::ostream_iterator<quantity<si::time> > out(std::cout, "\n");
    std::copy(tester.begin(), tester.end(), out);
}

In Christ,
Steven Watanabe