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/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)
__anon5a0dd0bf0102(auto t) 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)
__anon5a0dd0bf0202(auto t) 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>
operator ()some_function58 void operator()(T&&) const { }
59 };
60
main()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 }
68