[libcxx-commits] [libcxx] [String] Allow fancy pointer as pointer type of basic_string allocator (PR #191023)

[A. Jiang via libcxx-commits]

================
@@ -444,6 +445,235 @@ TEST_CONSTEXPR_CXX20 thread_unsafe_shared_ptr<T> make_thread_unsafe_shared(Args.
 }
 } // namespace detail
 
+template <class T>
+class fancy_pointer {
+public:
+  // For the std::pointer_traits interface.
+  using pointer         = T*;
+  using element_type    = T;
+  using difference_type = std::ptrdiff_t;
+
+  template <class U>
+  using rebind = fancy_pointer<U>;
+
+  // For the std::iterator_traits interface.
+  using value_type        = typename std::remove_cv<T>::type;
+  using reference         = typename std::add_lvalue_reference<T>::type;
+  using iterator_category = std::random_access_iterator_tag;
+
+  TEST_CONSTEXPR_CXX14 fancy_pointer() TEST_NOEXCEPT : ptr_(nullptr) {}
+  TEST_CONSTEXPR_CXX14 fancy_pointer(T* p) TEST_NOEXCEPT : ptr_(p) {}
+
+  template <typename T2>
+  TEST_CONSTEXPR_CXX14 explicit fancy_pointer(const fancy_pointer<T2>& other) TEST_NOEXCEPT
+      : ptr_(static_cast<T*>(other.get())) {}
+
+  TEST_CONSTEXPR_CXX14 operator T*() const TEST_NOEXCEPT { return ptr_; }
+  TEST_CONSTEXPR_CXX14 fancy_pointer(fancy_pointer&&) TEST_NOEXCEPT                 = default;
+  TEST_CONSTEXPR_CXX14 fancy_pointer(const fancy_pointer&) TEST_NOEXCEPT            = default;
+  TEST_CONSTEXPR_CXX14 fancy_pointer& operator=(fancy_pointer&&) TEST_NOEXCEPT      = default;
+  TEST_CONSTEXPR_CXX14 fancy_pointer& operator=(const fancy_pointer&) TEST_NOEXCEPT = default;
+  TEST_CONSTEXPR_CXX20 ~fancy_pointer() TEST_NOEXCEPT                               = default;
----------------
frederick-vs-ja wrote:

These 5 special member functions are still trivial. Could we make them all non-trivial, but still `noexcept` and doing the same operations as defaulted ones?

https://github.com/llvm/llvm-project/pull/191023