ceph/src/boost/libs/hana/example/tutorial/introduction.cpp

   1 // Copyright Louis Dionne 2013-2016
   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 // Make sure `assert` always triggers an assertion
   6 #ifdef NDEBUG
   7 #   undef NDEBUG
   8 #endif
   9
  10 #include <boost/fusion/include/comparison.hpp>
  11 #include <boost/fusion/include/make_vector.hpp>
  12 #include <boost/fusion/include/transform.hpp>
  13 #include <boost/fusion/include/vector.hpp>
  14
  15 #include <boost/mpl/equal.hpp>
  16 #include <boost/mpl/placeholders.hpp>
  17 #include <boost/mpl/transform.hpp>
  18 #include <boost/mpl/vector.hpp>
  19
  20 #include <algorithm>
  21 #include <cassert>
  22 #include <iterator>
  23 #include <sstream>
  24 #include <string>
  25 #include <vector>
  26 namespace fusion = boost::fusion;
  27 namespace mpl = boost::mpl;
  28 using namespace std::literals;
  29
  30
  31 int main() {
  32
  33 {
  34
  35 //! [runtime]
  36 auto f = [](int i) -> std::string {
  37   return std::to_string(i * i);
  38 };
  39
  40 std::vector<int> ints{1, 2, 3, 4};
  41 std::vector<std::string> strings;
  42 std::transform(ints.begin(), ints.end(), std::back_inserter(strings), f);
  43
  44 assert((strings == std::vector<std::string>{"1", "4", "9", "16"}));
  45 //! [runtime]
  46
  47 }{
  48
  49 //! [heterogeneous]
  50 auto to_string = [](auto t) {
  51   std::stringstream ss;
  52   ss << t;
  53   return ss.str();
  54 };
  55
  56 fusion::vector<int, std::string, float> seq{1, "abc", 3.4f};
  57 fusion::vector<std::string, std::string, std::string>
  58   strings = fusion::transform(seq, to_string);
  59
  60 assert(strings == fusion::make_vector("1"s, "abc"s, "3.4"s));
  61 //! [heterogeneous]
  62
  63 }
  64
  65 }
  66
  67 //! [type-level]
  68 template <typename T>
  69 struct add_const_pointer {
  70   using type = T const*;
  71 };
  72
  73 using types = mpl::vector<int, char, float, void>;
  74 using pointers = mpl::transform<types, add_const_pointer<mpl::_1>>::type;
  75
  76 static_assert(mpl::equal<
  77   pointers,
  78   mpl::vector<int const*, char const*, float const*, void const*>
  79 >::value, "");
  80 //! [type-level]