[libcxx-commits] [libcxx] [libc++] Implement P2988R12: `std::optional<T&>` (PR #155202)

[William Tran-Viet via libcxx-commits]

================
@@ -628,21 +629,89 @@ public:
   using iterator       = __wrap_iter<__pointer>;
   using const_iterator = __wrap_iter<__const_pointer>;
 #      endif
+
+  // [optional.iterators], iterator support
+  _LIBCPP_HIDE_FROM_ABI constexpr iterator begin() noexcept {
+    auto& __derived_self = static_cast<optional<_Tp>&>(*this);
+    auto __ptr           = [&__derived_self]() {
+      if constexpr (is_lvalue_reference_v<_Tp>) {
+        return __derived_self.has_value() ? std::addressof(__derived_self.__get()) : nullptr;
+      }
+      return std::addressof(__derived_self.__get());
+    }();
+
+#      ifdef _LIBCPP_ABI_BOUNDED_ITERATORS_IN_OPTIONAL
+    return std::__make_bounded_iter(
+        std::__wrap_iter<__pointer>(__ptr),
+        std::__wrap_iter<__pointer>(__ptr),
+        std::__wrap_iter<__pointer>(__ptr) + (__derived_self.has_value() ? 1 : 0));
+#      else
+    return iterator(__ptr);
+#      endif
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr const_iterator begin() const noexcept {
+    auto& __derived_self = static_cast<const optional<_Tp>&>(*this);
+    auto* __ptr          = [&__derived_self]() {
+      if constexpr (is_lvalue_reference_v<_Tp>) {
+        return __derived_self.has_value() ? std::addressof(__derived_self.__get()) : nullptr;
+      }
+      return std::addressof(__derived_self.__get());
+    }();
+
+#      ifdef _LIBCPP_ABI_BOUNDED_ITERATORS_IN_OPTIONAL
+    return std::__make_bounded_iter(
+        std::__wrap_iter<__const_pointer>(__ptr),
+        std::__wrap_iter<__const_pointer>(__ptr),
+        std::__wrap_iter<__const_pointer>(__ptr) + (__derived_self.has_value() ? 1 : 0));
+#      else
+    return const_iterator(__ptr);
+#      endif
+  }
+
+  _LIBCPP_HIDE_FROM_ABI constexpr iterator end() noexcept {
+    return begin() + (static_cast<optional<_Tp>&>(*this).has_value() ? 1 : 0);
+  }
+  _LIBCPP_HIDE_FROM_ABI constexpr const_iterator end() const noexcept {
+    return begin() + (static_cast<const optional<_Tp>&>(*this).has_value() ? 1 : 0);
+  }
 #    endif
+};
+
+template <class _Tp>
+class _LIBCPP_DECLSPEC_EMPTY_BASES optional
+    : private __optional_move_assign_base<_Tp>,
+      private __optional_sfinae_ctor_base_t<_Tp>,
+      private __optional_sfinae_assign_base_t<_Tp>,
+      public __optional_iterator<_Tp> {
+  using __base _LIBCPP_NODEBUG = __optional_move_assign_base<_Tp>;
+
+public:
+  using value_type = _Tp;
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smallp-o-p wrote:

Oh, good catch, that doesn't happen.

https://github.com/llvm/llvm-project/pull/155202