1 // Copyright (C) 2019-2021 Free Software Foundation, Inc.
2 //
3 // This file is part of the GNU ISO C++ Library.  This library is free
4 // software; you can redistribute it and/or modify it under the
5 // terms of the GNU General Public License as published by the
6 // Free Software Foundation; either version 3, or (at your option)
7 // any later version.
8 
9 // This library is distributed in the hope that it will be useful,
10 // but WITHOUT ANY WARRANTY; without even the implied warranty of
11 // MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
12 // GNU General Public License for more details.
13 
14 // You should have received a copy of the GNU General Public License along
15 // with this library; see the file COPYING3.  If not see
16 // <http://www.gnu.org/licenses/>.
17 
18 // { dg-options "-std=gnu++2a" }
19 // { dg-do run { target c++2a } }
20 
21 #include <functional>
22 #include <memory>
23 #include <string>
24 #include <testsuite_hooks.h>
25 
26 // P1651R0 bind_front should not unwrap reference_wrapper
27 
28 #ifndef __cpp_lib_bind_front
29 # error "Feature test macro for bind_front is missing"
30 #elif __cpp_lib_bind_front < 201907L
31 # error "Feature test macro for bind_front has wrong value"
32 #endif
33 
functionAcceptingStringView(std::string_view)34 void functionAcceptingStringView(std::string_view) { }
35 
36 void
test01()37 test01()
38 {
39   std::string s;
40   auto fs = std::bind_front(&functionAcceptingStringView, std::string_view(s));
41   fs();
42 }
43 
44 template <typename F>
45 struct PartialApply {
PartialApplyPartialApply46     PartialApply(F f) : f(f) {}
47     F f;
48 
operator ()PartialApply49     template <typename... A> decltype(auto) operator()(A const&... a) const {
50         if constexpr (std::is_invocable<F const&, A const&...>::value) {
51             return f(a...);
52         } else {
53             return bind_front(*this, a...);
54         }
55     }
56 };
57 
58 void
test02()59 test02()
60 {
61   struct Thingy { };
62   std::unique_ptr<Thingy> thingy;
63   auto func = [](const std::unique_ptr<Thingy>&, int) {};
64   PartialApply{func}(std::ref(thingy))(10);
65 }
66 
67 void
test03()68 test03()
69 {
70   std::string str;
71   auto func = [](const std::string& s, int) -> const std::string& { return s; };
72 
73   // sref refers to copy of str stored in bind_front result:
74   const std::string& sref = PartialApply{func}(std::ref(str))(10);
75 
76   // pre-P1651R0 this is a use of a dangling reference:
77   const char& c = sref[0];
78 
79   // post-P1651R0 the bind_front result stores a reference_wrapper by value,
80   // and so sref is bound to str instead of dangling:
81   VERIFY( &c == str.data() );
82   VERIFY( &sref == &str );
83 }
84 
85 int
main()86 main()
87 {
88   test01();
89   test02();
90   test03();
91 }
92