ceph/src/boost/libs/hana/example/sequence/monad.types.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/chain.hpp>
   7 #include <boost/hana/equal.hpp>
   8 #include <boost/hana/for_each.hpp>
   9 #include <boost/hana/traits.hpp>
  10 #include <boost/hana/tuple.hpp>
  11 #include <boost/hana/type.hpp>
  12
  13 #include <type_traits>
  14 #include <utility>
  15 namespace hana = boost::hana;
  16
  17
  18 // Using the `tuple` Monad, we generate all the possible combinations of
  19 // cv-qualifiers and reference qualifiers. Then, we use the `optional`
  20 // Monad to make sure that our generic function can be called with
  21 // arguments of any of those types.
  22
  23 // cv_qualifiers : type -> tuple(type)
  24 auto cv_qualifiers = [](auto t) {
  25     return hana::make_tuple(
  26         t,
  27         hana::traits::add_const(t),
  28         hana::traits::add_volatile(t),
  29         hana::traits::add_volatile(hana::traits::add_const(t))
  30     );
  31 };
  32
  33 // ref_qualifiers : type -> tuple(type)
  34 auto ref_qualifiers = [](auto t) {
  35     return hana::make_tuple(
  36         hana::traits::add_lvalue_reference(t),
  37         hana::traits::add_rvalue_reference(t)
  38     );
  39 };
  40
  41 auto possible_args = cv_qualifiers(hana::type_c<int>) | ref_qualifiers;
  42
  43 BOOST_HANA_CONSTANT_CHECK(
  44     possible_args == hana::make_tuple(
  45                         hana::type_c<int&>,
  46                         hana::type_c<int&&>,
  47                         hana::type_c<int const&>,
  48                         hana::type_c<int const&&>,
  49                         hana::type_c<int volatile&>,
  50                         hana::type_c<int volatile&&>,
  51                         hana::type_c<int const volatile&>,
  52                         hana::type_c<int const volatile&&>
  53                     )
  54 );
  55
  56 struct some_function {
  57     template <typename T>
  58     void operator()(T&&) const { }
  59 };
  60
  61 int main() {
  62     hana::for_each(possible_args, [](auto t) {
  63         using T = typename decltype(t)::type;
  64         static_assert(decltype(hana::is_valid(some_function{})(std::declval<T>())){},
  65         "some_function should be callable with any type of argument");
  66     });
  67 }