llvm-project/libcxx/test/std/utilities/variant/variant.variant/variant.ctor/T.pass.cpp

//===----------------------------------------------------------------------===//
//
// Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
// See https://llvm.org/LICENSE.txt for license information.
// SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
//
//===----------------------------------------------------------------------===//

// UNSUPPORTED: c++03, c++11, c++14

// <variant>

// template <class ...Types> class variant;

// template <class T> constexpr variant(T&&) noexcept(see below);

#include <cassert>
#include <string>
#include <type_traits>
#include <variant>
#include <memory>
#include <vector>

#include "test_macros.h"
#include "variant_test_helpers.h"

struct Dummy {
  Dummy() = default;
};

struct ThrowsT {
  ThrowsT(int) noexcept(false) {}
};

struct NoThrowT {
  NoThrowT(int) noexcept(true) {}
};

struct AnyConstructible {
  template <typename T>
  AnyConstructible(T&&) {}
};
struct NoConstructible {
  NoConstructible() = delete;
};
template <class T>
struct RValueConvertibleFrom {
  RValueConvertibleFrom(T&&) {}
};

void test_T_ctor_noexcept() {
  {
    using V = std::variant<Dummy, NoThrowT>;
    static_assert(std::is_nothrow_constructible<V, int>::value, "");
  }
  {
    using V = std::variant<Dummy, ThrowsT>;
    static_assert(!std::is_nothrow_constructible<V, int>::value, "");
  }
}

void test_T_ctor_sfinae() {
  {
    using V = std::variant<long, long long>;
    static_assert(!std::is_constructible<V, int>::value, "ambiguous");
  }
  {
    using V = std::variant<std::string, std::string>;
    static_assert(!std::is_constructible<V, const char*>::value, "ambiguous");
  }
  {
    using V = std::variant<std::string, void*>;
    static_assert(!std::is_constructible<V, int>::value, "no matching constructor");
  }
  {
    using V = std::variant<std::string, float>;
    static_assert(!std::is_constructible<V, int>::value, "no matching constructor");
  }
  {
    using V = std::variant<std::unique_ptr<int>, bool>;
    static_assert(!std::is_constructible<V, std::unique_ptr<char>>::value, "no explicit bool in constructor");
    struct X {
      operator void*();
    };
    static_assert(!std::is_constructible<V, X>::value, "no boolean conversion in constructor");
    static_assert(std::is_constructible<V, std::false_type>::value, "converted to bool in constructor");
  }
  {
    struct X {};
    struct Y {
      operator X();
    };
    using V = std::variant<X>;
    static_assert(std::is_constructible<V, Y>::value, "regression on user-defined conversions in constructor");
  }
  {
    using V = std::variant<AnyConstructible, NoConstructible>;
    static_assert(!std::is_constructible<V, std::in_place_type_t<NoConstructible>>::value, "no matching constructor");
    static_assert(!std::is_constructible<V, std::in_place_index_t<1>>::value, "no matching constructor");
  }
}

void test_T_ctor_basic() {
  {
    constexpr std::variant<int> v(42);
    static_assert(v.index() == 0, "");
    static_assert(std::get<0>(v) == 42, "");
  }
  {
    constexpr std::variant<int, long> v(42l);
    static_assert(v.index() == 1, "");
    static_assert(std::get<1>(v) == 42, "");
  }
  {
    constexpr std::variant<unsigned, long> v(42);
    static_assert(v.index() == 1, "");
    static_assert(std::get<1>(v) == 42, "");
  }
  {
    std::variant<std::string, bool const> v = "foo";
    assert(v.index() == 0);
    assert(std::get<0>(v) == "foo");
  }
  {
    std::variant<bool, std::unique_ptr<int>> v = nullptr;
    assert(v.index() == 1);
    assert(std::get<1>(v) == nullptr);
  }
  {
    std::variant<bool const, int> v = true;
    assert(v.index() == 0);
    assert(std::get<0>(v));
  }
  {
    std::variant<RValueConvertibleFrom<int>> v1 = 42;
    assert(v1.index() == 0);

    int x                                                         = 42;
    std::variant<RValueConvertibleFrom<int>, AnyConstructible> v2 = x;
    assert(v2.index() == 1);
  }
}

struct BoomOnAnything {
  template <class T>
  constexpr BoomOnAnything(T) {
    static_assert(!std::is_same<T, T>::value, "");
  }
};

void test_no_narrowing_check_for_class_types() {
  using V = std::variant<int, BoomOnAnything>;
  V v(42);
  assert(v.index() == 0);
  assert(std::get<0>(v) == 42);
}

struct Bar {};
struct Baz {};
void test_construction_with_repeated_types() {
  using V = std::variant<int, Bar, Baz, int, Baz, int, int>;
  static_assert(!std::is_constructible<V, int>::value, "");
  static_assert(!std::is_constructible<V, Baz>::value, "");
  // OK, the selected type appears only once and so it shouldn't
  // be affected by the duplicate types.
  static_assert(std::is_constructible<V, Bar>::value, "");
}

void test_vector_bool() {
  std::vector<bool> vec = {true};
  std::variant<bool, int> v = vec[0];
  assert(v.index() == 0);
  assert(std::get<0>(v) == true);
}

struct ConvertibleFromAny {
  template <class V>
  ConvertibleFromAny(V) {}
};

int main(int, char**) {
  test_T_ctor_basic();
  test_T_ctor_noexcept();
  test_T_ctor_sfinae();
  test_no_narrowing_check_for_class_types();
  test_construction_with_repeated_types();
  test_vector_bool();

  { // Check that the constraints are evaluated lazily (see https://github.com/llvm/llvm-project/issues/151328)
    struct Matcher {
      Matcher() {}
      Matcher(std::variant<ConvertibleFromAny>) {}
    };

    Matcher vec;
    [[maybe_unused]] Matcher m = std::move(vec);
  }

  return 0;
}