libstdc++-v3/testsuite/20_util/function_objects/bind_front/2.cc

   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
  34 void functionAcceptingStringView(std::string_view) { }
  35
  36 void
  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 {
  46     PartialApply(F f) : f(f) {}
  47     F f;
  48
  49     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
  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
  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
  86 main()
  87 {
  88   test01();
  89   test02();
  90   test03();
  91 }