[libcxx] adds concept std::regular

[cjdb]

Summary

Implements parts of:

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

Depends on D97911

[• Quuxplusone]

libcxx/test/std/concepts/object/regular.compile.pass.cpp

13

s/From/T/

38

Here I think it would be more interesting to check some other built-in types — notably float/double, void*, and maybe even member-pointer-into-a-union-type (which supports operator== but with underspecified semantics).

You could pay for these new test cases by collapsing the 4 int*/int const*/int volatile*/int volatile const* lines into 1 line, and the following 25 lines into 1 line.

76

This line is out of place.
It did strike me tonight that we could have organized these tests completely differently: we could have presented one type at a time, and static-asserted exactly where it falls on the concept hierarchy. For example:

struct Simple {};
static_assert(std::semiregular<Simple> && !std::regular<Simple>);

struct MoveCtor { MoveCtor(MoveCtor&&); };
static_assert(std::move_constructible<MoveCtor> && !std::movable<MoveCtor>);

and so on.

[Mordante]

libcxx/test/std/concepts/object/regular.compile.pass.cpp

76

Isn't this done to show the type is semiregular, but not regular? There are more of these "double tests". But I agree combining them might be better.

121

Could these two also be combined?

[EricWF]

LGTM. I like Arthurs suggestion about the tests. But otherwise this change seems ready to go.

[cjdb]

applies @Quuxplusone's feedback

[• Quuxplusone]

libcxx/test/std/concepts/object/regular.compile.pass.cpp

145

/lz/liz/

148

/> >/>>/ since this test doesn't need C++03 portability

160

Should this say /On/No/?

[cjdb]

@Quuxplusone please check 8d4af1b.

libcxx/test/std/concepts/object/regular.compile.pass.cpp

148

clang-format issue, not arguing over this.

160

Both are semantically correct! I meant this as "on some topic of concern", but I think "no equality comparability" reads better here.

libcxx/include/concepts

concept copyable =
   movable<_Tp> &&
   assignable_from<_Tp&, _Tp&> &&
   assignable_from<_Tp&, const _Tp&> &&
   assignable_from<_Tp&, const _Tp>;
 
 template<class _Tp>
 concept semiregular = copyable<_Tp> && default_initializable<_Tp>;
 
+template<class _Tp>
+concept regular = semiregular<_Tp> && equality_comparable<_Tp>;
+
 // [concept.invocable]
 template<class _Fn, class... _Args>
 concept invocable = requires(_Fn&& __fn, _Args&&... __args) {
   _VSTD::invoke(_VSTD::forward<_Fn>(__fn), _VSTD::forward<_Args>(__args)...); // not required to be equality preserving
 };
 
 // [concept.regular.invocable]
 template<class _Fn, class... _Args>

libcxx/test/std/concepts/object/regular.compile.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, c++17
+// UNSUPPORTED: libcpp-no-concepts
+
+// template<class T>
+// concept regular = see below;
+
+#include <concepts>
+
+#include <deque>
+#include <forward_list>
+#include <list>
+#include <map>
+#include <memory>
+#include <optional>
+#include <stdexcept>
+#include <tuple>
+#include <unordered_map>
+#include <vector>
+
+#include "type_classification/moveconstructible.h"
+#include "type_classification/semiregular.h"
+
+static_assert(std::regular<int>);
+static_assert(std::regular<float>);
+static_assert(std::regular<double>);
+static_assert(std::regular<long double>);
+static_assert(std::regular<int volatile>);
+static_assert(std::regular<void*>);
+static_assert(std::regular<int*>);
+static_assert(std::regular<int const*>);
+static_assert(std::regular<int volatile*>);
+static_assert(std::regular<int volatile const*>);
+static_assert(std::regular<int (*)()>);
+
+struct S {};
+static_assert(!std::regular<S>);
+static_assert(std::regular<int S::*>);
+static_assert(std::regular<int (S::*)()>);
+static_assert(std::regular<int (S::*)() noexcept>);
+static_assert(std::regular<int (S::*)() &>);
+static_assert(std::regular<int (S::*)() & noexcept>);
+static_assert(std::regular<int (S::*)() &&>);
+static_assert(std::regular<int (S::*)() && noexcept>);
+static_assert(std::regular<int (S::*)() const>);
+static_assert(std::regular<int (S::*)() const noexcept>);
+static_assert(std::regular<int (S::*)() const&>);
+static_assert(std::regular<int (S::*)() const & noexcept>);
+static_assert(std::regular<int (S::*)() const&&>);
+static_assert(std::regular<int (S::*)() const && noexcept>);
+static_assert(std::regular<int (S::*)() volatile>);
+static_assert(std::regular<int (S::*)() volatile noexcept>);
+static_assert(std::regular<int (S::*)() volatile&>);
+static_assert(std::regular<int (S::*)() volatile & noexcept>);
+static_assert(std::regular<int (S::*)() volatile&&>);
+static_assert(std::regular<int (S::*)() volatile && noexcept>);
+static_assert(std::regular<int (S::*)() const volatile>);
+static_assert(std::regular<int (S::*)() const volatile noexcept>);
+static_assert(std::regular<int (S::*)() const volatile&>);
+static_assert(std::regular<int (S::*)() const volatile & noexcept>);
+static_assert(std::regular<int (S::*)() const volatile&&>);
+static_assert(std::regular<int (S::*)() const volatile && noexcept>);
+
+union U {};
+static_assert(!std::regular<U>);
+static_assert(std::regular<int U::*>);
+static_assert(std::regular<int (U::*)()>);
+static_assert(std::regular<int (U::*)() noexcept>);
+static_assert(std::regular<int (U::*)() &>);
+static_assert(std::regular<int (U::*)() & noexcept>);
+static_assert(std::regular<int (U::*)() &&>);
+static_assert(std::regular<int (U::*)() && noexcept>);
+static_assert(std::regular<int (U::*)() const>);
+static_assert(std::regular<int (U::*)() const noexcept>);
+static_assert(std::regular<int (U::*)() const&>);
+static_assert(std::regular<int (U::*)() const & noexcept>);
+static_assert(std::regular<int (U::*)() const&&>);
+static_assert(std::regular<int (U::*)() const && noexcept>);
+static_assert(std::regular<int (U::*)() volatile>);
+static_assert(std::regular<int (U::*)() volatile noexcept>);
+static_assert(std::regular<int (U::*)() volatile&>);
+static_assert(std::regular<int (U::*)() volatile & noexcept>);
+static_assert(std::regular<int (U::*)() volatile&&>);
+static_assert(std::regular<int (U::*)() volatile && noexcept>);
+static_assert(std::regular<int (U::*)() const volatile>);
+static_assert(std::regular<int (U::*)() const volatile noexcept>);
+static_assert(std::regular<int (U::*)() const volatile&>);
+static_assert(std::regular<int (U::*)() const volatile & noexcept>);
+static_assert(std::regular<int (U::*)() const volatile&&>);
+static_assert(std::regular<int (U::*)() const volatile && noexcept>);
+
+static_assert(std::regular<std::vector<int> >);
+static_assert(std::regular<std::deque<int> >);
+static_assert(std::regular<std::forward_list<int> >);
+static_assert(std::regular<std::list<int> >);
+static_assert(std::regular<std::shared_ptr<std::unique_ptr<int> > >);
+static_assert(std::regular<std::optional<std::vector<int> > >);
+static_assert(std::regular<std::vector<int> >);
+static_assert(std::regular<std::vector<std::unique_ptr<int> > >);
+static_assert(std::semiregular<std::in_place_t> &&
+              !std::regular<std::in_place_t>);
+
+static_assert(!std::regular<has_volatile_member>);
+static_assert(!std::regular<has_array_member>);
+
+// Not objects
+static_assert(!std::regular<void>);
+static_assert(!std::regular<int&>);
+static_assert(!std::regular<int const&>);
+static_assert(!std::regular<int volatile&>);
+static_assert(!std::regular<int const volatile&>);
+static_assert(!std::regular<int&&>);
+static_assert(!std::regular<int const&&>);
+static_assert(!std::regular<int volatile&&>);
+static_assert(!std::regular<int const volatile&&>);
+static_assert(!std::regular<int()>);
+static_assert(!std::regular<int (&)()>);
+static_assert(!std::regular<int[5]>);
+
+// not copyable
+static_assert(!std::regular<std::unique_ptr<int> >);
+static_assert(!std::regular<int const>);
+static_assert(!std::regular<int const volatile>);
+static_assert(!std::regular<volatile_copy_assignment volatile>);
+static_assert(!std::regular<no_copy_constructor>);
+static_assert(!std::regular<no_copy_assignment>);
+static_assert(!std::regular<no_copy_assignment_mutable>);
+static_assert(!std::regular<derived_from_noncopyable>);
+static_assert(!std::regular<has_noncopyable>);
+static_assert(!std::regular<has_const_member>);
+static_assert(!std::regular<has_cv_member>);
+static_assert(!std::regular<has_lvalue_reference_member>);
+static_assert(!std::regular<has_rvalue_reference_member>);
+static_assert(!std::regular<has_function_ref_member>);
+static_assert(!std::regular<deleted_assignment_from_const_rvalue>);
+
+// not default_initializable
+static_assert(!std::regular<std::runtime_error>);
+static_assert(
+    !std::regular<std::tuple<std::runtime_error, std::overflow_error> >);
+static_assert(!std::regular<std::nullopt_t>);
+static_assert(!std::regular<no_copy_constructor>);
+static_assert(!std::regular<no_copy_assignment>);
+static_assert(std::is_copy_assignable_v<no_copy_assignment_mutable> &&
+              !std::regular<no_copy_assignment_mutable>);
+static_assert(!std::regular<derived_from_noncopyable>);
+static_assert(!std::regular<has_noncopyable>);
+
+static_assert(!std::regular<derived_from_non_default_initializable>);
+static_assert(!std::regular<has_non_default_initializable>);
+
+// not equality_comparable
+static_assert(!std::regular<const_copy_assignment const>);
+static_assert(!std::regular<cv_copy_assignment const volatile>);
+
+struct is_equality_comparable {
+  [[nodiscard]] bool operator==(is_equality_comparable const&) const = default;
+};
+static_assert(std::regular<is_equality_comparable>);
+
+int main(int, char**) { return 0; }