1 // Copyright (c) 2019-2021 Antony Polukhin.
2 //
3 // Distributed under the Boost Software License, Version 1.0. (See accompanying
4 // file LICENSE_1_0.txt or copy at http://www.boost.org/LICENSE_1_0.txt)
5
6 #include <type_traits>
7
8 #include <boost/pfr/core.hpp>
9
10 template <class T>
11 struct constrained_template {
12 constrained_template() = default;
13
14 template <
15 class U = T,
16 std::enable_if_t<
17 std::is_constructible<T, U&&>::value
18 || sizeof(decltype(T{std::declval<U&&>()}))
19 , bool> = false>
constrained_templateconstrained_template20 constexpr constrained_template(U&& val)
21 : value_{std::forward<U>(val)}
22 {}
23
24 T value_;
25 };
26
27 struct int_element {
28 int value_;
29 };
30
31 struct aggregate_constrained {
32 constrained_template<short> a;
33 constrained_template<int_element> b;
34 };
35
main()36 int main() {
37 static_assert(
38 std::is_same<
39 boost::pfr::tuple_element_t<0, aggregate_constrained>,
40 constrained_template<short>
41 >::value,
42 "Precise reflection with template constructors fails to work"
43 );
44
45 static_assert(
46 std::is_same<
47 boost::pfr::tuple_element_t<1, aggregate_constrained>,
48 constrained_template<int_element>
49 >::value,
50 "Precise reflection with template constructors fails to work"
51 );
52
53 short s = 3;
54 aggregate_constrained aggr{s, 4};
55 return boost::pfr::get<1>(aggr).value_.value_ - 4;
56 }
57