libcxx/test/std/utilities/variant/variant.visit/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
  10
  11 // <variant>
  12 // template <class Visitor, class... Variants>
  13 // constexpr see below visit(Visitor&& vis, Variants&&... vars);
  14
  15 #include <variant>
  16
  17 #include "test_macros.h"
  18
  19 struct Incomplete;
  20 template<class T> struct Holder { T t; };
  21
  22 constexpr bool test(bool do_it)
  23 {
  24     if (do_it) {
  25         std::variant<Holder<Incomplete>*, int> v = nullptr;
  26         std::visit([](auto){}, v);
  27         std::visit([](auto) -> Holder<Incomplete>* { return nullptr; }, v);
  28 #if TEST_STD_VER > 17
  29         std::visit<void>([](auto){}, v);
  30         std::visit<void*>([](auto) -> Holder<Incomplete>* { return nullptr; }, v);
  31 #endif
  32     }
  33     return true;
  34 }
  35
  36 int main(int, char**)
  37 {
  38     test(true);
  39 #if TEST_STD_VER > 17
  40     static_assert(test(true));
  41 #endif
  42     return 0;
  43 }