libcxx/test/std/utilities/variant/variant.visit.member/robust_against_adl.pass.cpp

   1 //===----------------------------------------------------------------------===//
   2 //
   3 // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
   4 // See https://llvm.org/LICENSE.txt for license information.
   5 // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
   6 //
   7 //===----------------------------------------------------------------------===//
   8
   9 // UNSUPPORTED: c++03, c++11, c++14, c++17, c++20, c++23
  10 // The tested functionality needs deducing this.
  11 // UNSUPPORTED: clang-17
  12 // XFAIL: apple-clang
  13
  14 // <variant>
  15
  16 // class variant;
  17 // template<class Self, class Visitor>
  18 //   constexpr decltype(auto) visit(this Self&&, Visitor&&); // since C++26
  19 // template<class R, class Self, class Visitor>
  20 //   constexpr R visit(this Self&&, Visitor&&);              // since C++26
  21
  22 #include <variant>
  23
  24 #include "test_macros.h"
  25
  26 struct Incomplete;
  27 template <class T>
  28 struct Holder {
  29   T t;
  30 };
  31
  32 constexpr bool test(bool do_it) {
  33   if (do_it) {
  34     std::variant<Holder<Incomplete>*, int> v = nullptr;
  35
  36     v.visit([](auto) {});
  37     v.visit([](auto) -> Holder<Incomplete>* { return nullptr; });
  38     v.visit<void>([](auto) {});
  39     v.visit<void*>([](auto) -> Holder<Incomplete>* { return nullptr; });
  40   }
  41   return true;
  42 }
  43
  44 int main(int, char**) {
  45   test(true);
  46   static_assert(test(true));
  47
  48   return 0;
  49 }