ceph/src/boost/libs/hana/example/tutorial/constant_side_effects.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/bool.hpp>
   6
   7 #include <iostream>
   8 namespace hana = boost::hana;
   9
  10
  11 namespace pure {
  12 //! [pure]
  13 template <typename X>
  14 auto identity(X x) { return x; }
  15
  16 auto x = identity(hana::bool_c<true>);
  17 static_assert(hana::value(x), "");
  18 //! [pure]
  19 }
  20
  21 namespace impure {
  22 //! [impure_identity]
  23 template <typename X>
  24 auto identity(X x) {
  25     std::cout << "Good luck in evaluating this at compile-time!";
  26     return x;
  27 }
  28 //! [impure_identity]
  29
  30 //! [impure]
  31 auto x = identity(hana::bool_c<true>);
  32 static_assert(hana::value(x), "");
  33 //! [impure]
  34 }
  35
  36 int main() { }