[libcxx] adds concept `std::move_constructible`

[cjdb]

Summary

Implements parts of:

• P0898R3 Standard Library Concepts
• P1754 Rename concepts to standard_case for C++20, while we still can

Depends on D77961

[cjdb]

updates commit message to indicate dependency

[Mordante]

Do we need to do some tests on
[concept.moveconstructible]/1 http://eel.is/c++draft/concepts#concept.moveconstructible-1 ? Or does constructible_­from and convertible_­to guarantee these conditions hold?

libcxx/test/std/concepts/lang/moveconstructible.pass.cpp

8

Since the tests only has static_asserts it could be made a compile-time test. That can be done by renaming the file to move_constructible.compile.pass.cpp

13

This seems to be a copy-paste. move_constructible has only one template argument.

[cjdb]

applies @Mordante's suggestions

[cjdb]

adds new line to EOF

[cjdb]

In D96230#2548903, @Mordante wrote:

Do we need to do some tests on
[concept.moveconstructible]/1 http://eel.is/c++draft/concepts#concept.moveconstructible-1 ? Or does constructible_­from and convertible_­to guarantee these conditions hold?

The compiler doesn't check the semantic requirements (right now), so there's nothing to test. If we decide to promote violating the semantic requirements from IFNDR to ill-formed, that's when adding the tests will be helpful (right now they'd likely get in the way).

[Mordante]

In D96230#2550352, @cjdb wrote:

In D96230#2548903, @Mordante wrote:

Do we need to do some tests on
[concept.moveconstructible]/1 http://eel.is/c++draft/concepts#concept.moveconstructible-1 ? Or does constructible_­from and convertible_­to guarantee these conditions hold?

The compiler doesn't check the semantic requirements (right now), so there's nothing to test. If we decide to promote violating the semantic requirements from IFNDR to ill-formed, that's when adding the tests will be helpful (right now they'd likely get in the way).

SGTM. Just a bit surprised the Standard doesn't require more tests. Especially surprised by std::invocable and std::regular_invocable that they're the same. But I assume it has something to do with hard to validate.

No more comment, so LGTM.

[ldionne]

LGTM after you've considered my comments. You can update the review if you want to re-trigger CI, but no need to wait for my approval. This is great, thanks!

libcxx/test/std/concepts/lang/moveconstructible.compile.pass.cpp

1 ↗

(On Diff #322283)

Should this test be named move_constructible.compile.pass.cpp instead?

21 ↗

(On Diff #322283)

You can move those out of main() since they are just static_asserts.

libcxx/test/std/concepts/lang/moveconstructible.h

8 ↗

(On Diff #322283)

Please use TEST_STD_CONCEPTS_LAND_MOVECONSTRUCTIBLE_H or something that more clearly encodes the path of the file. Nitpicky :-)

[ldionne]

libcxx/test/std/concepts/lang/moveconstructible.compile.pass.cpp

1 ↗

(On Diff #322283)

Ahh, I see, you've named them after the section in the standard. LGTM

[cjdb]

applies @ldionne's feedback

libcxx/include/concepts

 
 template<class _Tp>
 concept __default_initializable = requires { ::new _Tp; };
 
 template<class _Tp>
 concept default_initializable = constructible_from<_Tp> &&
     requires { _Tp{}; } && __default_initializable<_Tp>;
 
+// [concept.moveconstructible]
+template<class _Tp>
+concept move_constructible =
+  constructible_from<_Tp, _Tp> && convertible_to<_Tp, _Tp>;
+
 #endif //_LIBCPP_STD_VER > 17 && defined(__cpp_concepts) && __cpp_concepts >= 201811L
 
 _LIBCPP_END_NAMESPACE_STD
 
 _LIBCPP_POP_MACROS
 
 #endif // _LIBCPP_CONCEPTS

libcxx/test/std/concepts/lang/moveconstructible.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++98, c++03, c++11, c++14, c++17
+// UNSUPPORTED: libcpp-no-concepts
+
+// template<class From, class To>
+// concept move_constructible;
+
+#include <concepts>
+#include <type_traits>
+
+struct HasDefaultOps {};
+
+struct CustomMoveCtor {
+  CustomMoveCtor(CustomMoveCtor&&) noexcept;
+};
+
+struct MoveOnly {
+  MoveOnly(MoveOnly&&) noexcept = default;
+  MoveOnly& operator=(MoveOnly&&) noexcept = default;
+  MoveOnly(const MoveOnly&) = delete;
+  MoveOnly& operator=(const MoveOnly&) = default;
+};
+
+struct CustomMoveAssign {
+  CustomMoveAssign(CustomMoveAssign&&) noexcept;
+  CustomMoveAssign& operator=(CustomMoveAssign&&) noexcept;
+};
+
+struct DeletedMoveCtor {
+  DeletedMoveCtor(DeletedMoveCtor&&) = delete;
+};
+
+struct ImplicitlyDeletedMoveCtor {
+  DeletedMoveCtor X;
+};
+
+struct DeletedMoveAssign {
+  DeletedMoveAssign& operator=(DeletedMoveAssign&&) = default;
+};
+
+struct ImplicitlyDeletedMoveAssign {
+  DeletedMoveAssign X;
+};
+
+class MemberLvalueReference {
+public:
+  MemberLvalueReference(int&);
+
+private:
+  int& X;
+};
+
+class MemberRvalueReference {
+public:
+  MemberRvalueReference(int&&);
+
+private:
+  int&& X;
+};
+
+int main(int, char**) {
+  static_assert(std::move_constructible<int>);
+  static_assert(std::move_constructible<int*>);
+  static_assert(std::move_constructible<int&>);
+  static_assert(std::move_constructible<int&&>);
+  static_assert(std::move_constructible<const int>);
+  static_assert(std::move_constructible<const int&>);
+  static_assert(std::move_constructible<const int&&>);
+  static_assert(std::move_constructible<volatile int>);
+  static_assert(std::move_constructible<volatile int&>);
+  static_assert(std::move_constructible<volatile int&&>);
+  static_assert(std::move_constructible<int (*)()>);
+  static_assert(std::move_constructible<int (&)()>);
+  static_assert(std::move_constructible<HasDefaultOps>);
+  static_assert(std::move_constructible<CustomMoveCtor>);
+  static_assert(std::move_constructible<MoveOnly>);
+  static_assert(std::move_constructible<const CustomMoveCtor&>);
+  static_assert(std::move_constructible<volatile CustomMoveCtor&>);
+  static_assert(std::move_constructible<const CustomMoveCtor&&>);
+  static_assert(std::move_constructible<volatile CustomMoveCtor&&>);
+  static_assert(std::move_constructible<CustomMoveAssign>);
+  static_assert(std::move_constructible<const CustomMoveAssign&>);
+  static_assert(std::move_constructible<volatile CustomMoveAssign&>);
+  static_assert(std::move_constructible<const CustomMoveAssign&&>);
+  static_assert(std::move_constructible<volatile CustomMoveAssign&&>);
+  static_assert(std::move_constructible<int HasDefaultOps::*>);
+  static_assert(std::move_constructible<void (HasDefaultOps::*)(int)>);
+  static_assert(std::move_constructible<MemberLvalueReference>);
+  static_assert(std::move_constructible<MemberRvalueReference>);
+
+  static_assert(!std::move_constructible<void>);
+  static_assert(!std::move_constructible<const CustomMoveCtor>);
+  static_assert(!std::move_constructible<volatile CustomMoveCtor>);
+  static_assert(!std::move_constructible<const CustomMoveAssign>);
+  static_assert(!std::move_constructible<volatile CustomMoveAssign>);
+  static_assert(!std::move_constructible<int[10]>);
+  static_assert(!std::move_constructible<DeletedMoveCtor>);
+  static_assert(!std::move_constructible<ImplicitlyDeletedMoveCtor>);
+  static_assert(!std::move_constructible<DeletedMoveAssign>);
+  static_assert(!std::move_constructible<ImplicitlyDeletedMoveAssign>);
+
+  static_assert(std::move_constructible<DeletedMoveCtor&>);
+  static_assert(std::move_constructible<DeletedMoveCtor&&>);
+  static_assert(std::move_constructible<const DeletedMoveCtor&>);
+  static_assert(std::move_constructible<const DeletedMoveCtor&&>);
+  static_assert(std::move_constructible<ImplicitlyDeletedMoveCtor&>);
+  static_assert(std::move_constructible<ImplicitlyDeletedMoveCtor&&>);
+  static_assert(std::move_constructible<const ImplicitlyDeletedMoveCtor&>);
+  static_assert(std::move_constructible<const ImplicitlyDeletedMoveCtor&&>);
+  static_assert(std::move_constructible<DeletedMoveAssign&>);
+  static_assert(std::move_constructible<DeletedMoveAssign&&>);
+  static_assert(std::move_constructible<const DeletedMoveAssign&>);
+  static_assert(std::move_constructible<const DeletedMoveAssign&&>);
+  static_assert(std::move_constructible<ImplicitlyDeletedMoveAssign&>);
+  static_assert(std::move_constructible<ImplicitlyDeletedMoveAssign&&>);
+  static_assert(std::move_constructible<const ImplicitlyDeletedMoveAssign&>);
+  static_assert(std::move_constructible<const ImplicitlyDeletedMoveAssign&&>);
+  return 0;
+}