ceph/src/boost/libs/hana/example/extend.cpp

   1 // Copyright Louis Dionne 2013-2017
   2 // Distributed under the Boost Software License, Version 1.0.
   3 // (See accompanying file LICENSE.md or copy at http://boost.org/LICENSE_1_0.txt)
   4
   5 #include <boost/hana/assert.hpp>
   6 #include <boost/hana/eval.hpp>
   7 #include <boost/hana/extend.hpp>
   8 #include <boost/hana/extract.hpp>
   9 #include <boost/hana/lazy.hpp>
  10
  11 #include <functional>
  12 #include <istream>
  13 #include <sstream>
  14 namespace hana = boost::hana;
  15
  16
  17 template <typename T>
  18 T read_one(std::istream& s) {
  19     T value;
  20     s >> value;
  21     return value;
  22 }
  23
  24 int main() {
  25     std::stringstream s;
  26     s << "1 2 3";
  27
  28     auto from_stream = hana::extend(hana::make_lazy(read_one<int>)(std::ref(s)), [](auto i) {
  29         return hana::eval(i) + 1;
  30     });
  31
  32     BOOST_HANA_RUNTIME_CHECK(hana::extract(from_stream) == 2);
  33     BOOST_HANA_RUNTIME_CHECK(hana::extract(from_stream) == 3);
  34     BOOST_HANA_RUNTIME_CHECK(hana::extract(from_stream) == 4);
  35 }