[libcxx-commits] [libcxx] [libc++] Decouple `optional<T>` and `optional<T&>` base classes (PR #215012)
William Tran-Viet via libcxx-commits
libcxx-commits at lists.llvm.org
Sat Aug 8 12:43:01 PDT 2026
https://github.com/smallp-o-p created https://github.com/llvm/llvm-project/pull/215012
- Remove the shared `__optional_storage_base` base class and associated partial specializations to handle the `T&` case in `optional<T>`
- Refactor and rename `optional<T&>`'s base classes.
>From 76da03f5c3f475c241cb12ed58db39a327a956ec Mon Sep 17 00:00:00 2001
From: William Tran-Viet <wtranviet at proton.me>
Date: Fri, 7 Aug 2026 16:19:10 -0400
Subject: [PATCH 1/2] [libc++] Decouple `optional<T>` and `optional<T&>` base
classes
---
libcxx/include/__optional/common.h | 3 --
libcxx/include/__optional/optional.h | 2 +-
libcxx/include/__optional/optional_ref.h | 49 ++++++++++--------------
3 files changed, 22 insertions(+), 32 deletions(-)
diff --git a/libcxx/include/__optional/common.h b/libcxx/include/__optional/common.h
index 5ddb993f3e376..26031f658a904 100644
--- a/libcxx/include/__optional/common.h
+++ b/libcxx/include/__optional/common.h
@@ -64,9 +64,6 @@ inline constexpr bool __is_std_optional_v = false;
template <class _Tp>
inline constexpr bool __is_std_optional_v<optional<_Tp>> = true;
-template <class _Tp, bool = is_reference<_Tp>::value>
-struct __optional_storage_base;
-
# if _LIBCPP_STD_VER < 26
template <class _Tp>
inline constexpr bool __is_valid_optional_contained_type = is_object_v<_Tp>;
diff --git a/libcxx/include/__optional/optional.h b/libcxx/include/__optional/optional.h
index 8d6a9fbed8599..3cadbae1fcf14 100644
--- a/libcxx/include/__optional/optional.h
+++ b/libcxx/include/__optional/optional.h
@@ -136,7 +136,7 @@ struct __optional_destruct_base<_Tp, true> {
}
};
-template <class _Tp, bool>
+template <class _Tp>
struct __optional_storage_base : __optional_destruct_base<_Tp> {
using __base _LIBCPP_NODEBUG = __optional_destruct_base<_Tp>;
using value_type = _Tp;
diff --git a/libcxx/include/__optional/optional_ref.h b/libcxx/include/__optional/optional_ref.h
index d137b3c40c7e6..e99fc8cf8f143 100644
--- a/libcxx/include/__optional/optional_ref.h
+++ b/libcxx/include/__optional/optional_ref.h
@@ -49,17 +49,17 @@
_LIBCPP_PUSH_MACROS
#include <__undef_macros>
-#if _LIBCPP_STD_VER >= 17
+#if _LIBCPP_STD_VER >= 26
_LIBCPP_BEGIN_NAMESPACE_STD
template <class _Tp>
-struct __optional_storage_base<_Tp, true> {
+struct __optional_ref_base {
using value_type = _Tp;
using __raw_type _LIBCPP_NODEBUG = remove_reference_t<_Tp>;
__raw_type* __value_;
- _LIBCPP_HIDE_FROM_ABI constexpr __optional_storage_base() noexcept : __value_(nullptr) {}
+ _LIBCPP_HIDE_FROM_ABI constexpr __optional_ref_base() noexcept : __value_(nullptr) {}
template <class _Up>
_LIBCPP_HIDE_FROM_ABI constexpr void __convert_init_ref_val(_Up&& __val) {
@@ -68,7 +68,7 @@ struct __optional_storage_base<_Tp, true> {
}
template <class _UArg>
- _LIBCPP_HIDE_FROM_ABI constexpr explicit __optional_storage_base(in_place_t, _UArg&& __uarg) {
+ _LIBCPP_HIDE_FROM_ABI constexpr explicit __optional_ref_base(in_place_t, _UArg&& __uarg) {
static_assert(!__reference_constructs_from_temporary_v<_Tp, _UArg>,
"Attempted to construct a reference element in optional from a "
"possible temporary");
@@ -77,7 +77,7 @@ struct __optional_storage_base<_Tp, true> {
# if _LIBCPP_STD_VER >= 23
template <class _Fp, class... _Args>
- constexpr __optional_storage_base(__optional_construct_from_invoke_tag, _Fp&& __f, _Args&&... __args) {
+ constexpr __optional_ref_base(__optional_construct_from_invoke_tag, _Fp&& __f, _Args&&... __args) {
__convert_init_ref_val(std::forward<invoke_result_t<_Fp, _Args...>>(
std::invoke(std::forward<_Fp>(__f), std::forward<_Args>(__args)...)));
}
@@ -116,7 +116,7 @@ struct __optional_storage_base<_Tp, true> {
}
}
- _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __swap(__optional_storage_base& __rhs) noexcept {
+ _LIBCPP_HIDE_FROM_ABI _LIBCPP_CONSTEXPR_SINCE_CXX20 void __swap(__optional_ref_base& __rhs) noexcept {
std::swap(__value_, __rhs.__value_);
}
@@ -138,43 +138,38 @@ struct __optional_storage_base<_Tp, true> {
}
};
-# if _LIBCPP_STD_VER >= 26
-
-template <class _Tp>
-struct __optional_iterator_base;
-
template <class _Tp>
-struct __optional_iterator_base<_Tp&> : __optional_storage_base<_Tp&> {
- using __optional_storage_base<_Tp&>::__optional_storage_base;
+struct __optional_ref_iterator_base : __optional_ref_base<_Tp&> {
+ using __optional_ref_base<_Tp&>::__optional_ref_base;
};
-# if _LIBCPP_HAS_EXPERIMENTAL_OPTIONAL_ITERATOR
+# if _LIBCPP_HAS_EXPERIMENTAL_OPTIONAL_ITERATOR
template <class _Tp>
requires(is_object_v<_Tp> && !__is_unbounded_array_v<_Tp>)
-struct __optional_iterator_base<_Tp&> : __optional_storage_base<_Tp&> {
+struct __optional_ref_iterator_base<_Tp&> : __optional_ref_base<_Tp&> {
private:
using __pointer _LIBCPP_NODEBUG = add_pointer_t<_Tp>;
public:
- using __optional_storage_base<_Tp&>::__optional_storage_base;
+ using __optional_ref_base<_Tp&>::__optional_ref_base;
-# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS_IN_OPTIONAL
+# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS_IN_OPTIONAL
using iterator = __bounded_iter<__pointer>;
-# else
+# else
using iterator = __capacity_aware_iterator<__pointer, optional<_Tp&>, 1>;
-# endif
+# endif
// [optional.ref.iterators], iterator support
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto begin() const noexcept {
auto* __ptr = this->has_value() ? std::addressof(this->__get()) : nullptr;
-# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS_IN_OPTIONAL
+# ifdef _LIBCPP_ABI_BOUNDED_ITERATORS_IN_OPTIONAL
return std::__make_bounded_iter(__ptr, __ptr, __ptr + (this->has_value() ? 1 : 0));
-# else
+# else
return std::__make_capacity_aware_iterator<__pointer, optional<_Tp&>, 1>(__ptr);
-# endif
+# endif
}
[[nodiscard]] _LIBCPP_HIDE_FROM_ABI constexpr auto end() const noexcept {
@@ -182,11 +177,11 @@ struct __optional_iterator_base<_Tp&> : __optional_storage_base<_Tp&> {
}
};
-# endif
+# endif
template <class _Tp>
-class optional<_Tp&> : public __optional_iterator_base<_Tp&> {
- using __base _LIBCPP_NODEBUG = __optional_iterator_base<_Tp&>;
+class optional<_Tp&> : public __optional_ref_iterator_base<_Tp&> {
+ using __base _LIBCPP_NODEBUG = __optional_ref_iterator_base<_Tp&>;
template <class _Up, class _QualUp>
static constexpr bool __check_optionalU_ctor =
@@ -346,11 +341,9 @@ class optional<_Tp&> : public __optional_iterator_base<_Tp&> {
using __base::reset;
};
-# endif // _LIBCPP_STD_VER >= 26
-
_LIBCPP_END_NAMESPACE_STD
-#endif // _LIBCPP_STD_VER >= 17
+#endif // _LIBCPP_STD_VER >= 26
_LIBCPP_POP_MACROS
>From 0e679078af8f75b00b5448a3c5c80dbef6605873 Mon Sep 17 00:00:00 2001
From: William Tran-Viet <wtranviet at proton.me>
Date: Sat, 8 Aug 2026 15:37:28 -0400
Subject: [PATCH 2/2] Fix static assert error message
---
libcxx/include/__optional/optional.h | 15 ++++++++++-----
1 file changed, 10 insertions(+), 5 deletions(-)
diff --git a/libcxx/include/__optional/optional.h b/libcxx/include/__optional/optional.h
index 3cadbae1fcf14..7955ea2812d32 100644
--- a/libcxx/include/__optional/optional.h
+++ b/libcxx/include/__optional/optional.h
@@ -73,6 +73,11 @@ struct __optional_destruct_base;
template <class _Tp>
struct __optional_destruct_base<_Tp, false> {
typedef _Tp value_type;
+# if _LIBCPP_STD_VER >= 26
+ static_assert(!is_rvalue_reference_v<_Tp>, "instantiation of optional with an rvalue reference type is ill-formed");
+# else
+ static_assert(!is_reference_v<_Tp>, "instantiation of optional with a reference type is ill-formed");
+# endif
static_assert(is_object_v<value_type>, "instantiation of optional with a non-object type is undefined behavior");
union {
char __null_state_;
@@ -109,6 +114,11 @@ struct __optional_destruct_base<_Tp, false> {
template <class _Tp>
struct __optional_destruct_base<_Tp, true> {
typedef _Tp value_type;
+# if _LIBCPP_STD_VER >= 26
+ static_assert(!is_rvalue_reference_v<_Tp>, "instantiation of optional with an rvalue reference type is ill-formed");
+# else
+ static_assert(!is_reference_v<_Tp>, "instantiation of optional with a reference type is ill-formed");
+# endif
static_assert(is_object_v<value_type>, "instantiation of optional with a non-object type is undefined behavior");
union {
char __null_state_;
@@ -419,11 +429,6 @@ class _LIBCPP_DECLSPEC_EMPTY_BASES optional
private:
static_assert(!is_same_v<remove_cv_t<_Tp>, in_place_t>, "instantiation of optional with in_place_t is ill-formed");
static_assert(!is_same_v<remove_cv_t<_Tp>, nullopt_t>, "instantiation of optional with nullopt_t is ill-formed");
-# if _LIBCPP_STD_VER >= 26
- static_assert(!is_rvalue_reference_v<_Tp>, "instantiation of optional with an rvalue reference type is ill-formed");
-# else
- static_assert(!is_reference_v<_Tp>, "instantiation of optional with a reference type is ill-formed");
-# endif
static_assert(is_destructible_v<_Tp>, "instantiation of optional with a non-destructible type is ill-formed");
static_assert(!is_array_v<_Tp>, "instantiation of optional with an array type is ill-formed");
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