Transform Iterator Lazy View for @jakepruitt

xform.cc

#include <iostream>
#include <vector>
#include <utility>

#include <boost/iterator/transform_iterator.hpp>

// Takes arbitrary [first,last) iterator range, returns pair of [first,last)-transform iterators applying fn on the fly
template <typename Iter>
auto xform(Iter first, Iter last) {
  // dummy function requiring values in the range to be convertible with to_string
  auto fn = [](auto v){ return std::to_string(v); };

  // lazy [first,last) transform iterator range, nothing is done so far
  auto tfirst = boost::make_transform_iterator(first, fn);
  auto tlast = boost::make_transform_iterator(last, fn);

  return make_pair(tfirst, tlast);
}


int main() {
  std::vector<int> v{10, 2, 30, 4};

  auto range = xform(begin(v), end(v));

  // only now the function is getting applied on the fly
  for (auto it = range.first; it != range.second; ++it)
    std::cout << it->size() << std::endl;
    // note how we can do ->size() since it's a std::string now because we apply fn on the fly taking int and returning std::string
}

http://www.boost.org/doc/libs/1_61_0/libs/iterator/doc/transform_iterator.html