ceph/src/boost/libs/hana/example/reverse_fold.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 #include <boost/hana/assert.hpp>
   6 #include <boost/hana/reverse_fold.hpp>
   7 #include <boost/hana/tuple.hpp>
   8
   9 #include <sstream>
  10 #include <string>
  11 namespace hana = boost::hana;
  12
  13
  14 auto to_string = [](auto x) {
  15     std::ostringstream ss;
  16     ss << x;
  17     return ss.str();
  18 };
  19
  20 int main() {
  21     auto f = [=](std::string s, auto element) {
  22         return "f(" + s + ", " + to_string(element) + ")";
  23     };
  24
  25     // With an initial state
  26     BOOST_HANA_RUNTIME_CHECK(
  27         hana::reverse_fold(hana::make_tuple(1, '2', 3.0, 4), "5", f)
  28             ==
  29         "f(f(f(f(5, 4), 3), 2), 1)"
  30     );
  31
  32     // Without an initial state
  33     BOOST_HANA_RUNTIME_CHECK(
  34         hana::reverse_fold(hana::make_tuple(1, '2', 3.0, 4, "5"), f)
  35             ==
  36         "f(f(f(f(5, 4), 3), 2), 1)"
  37     );
  38 }