[libcxx-commits] [libcxx] [libc++] Avoid type-punning between __value_type and pair (PR #134819)

[Louis Dionne via libcxx-commits]

================
@@ -763,64 +756,7 @@ class __map_const_iterator;
 #  ifndef _LIBCPP_CXX03_LANG
 
 template <class _Key, class _Tp>
-struct _LIBCPP_STANDALONE_DEBUG __value_type {
-  typedef _Key key_type;
-  typedef _Tp mapped_type;
-  typedef pair<const key_type, mapped_type> value_type;
-  typedef pair<key_type&, mapped_type&> __nc_ref_pair_type;
-  typedef pair<key_type&&, mapped_type&&> __nc_rref_pair_type;
-
-private:
-  value_type __cc_;
-
-public:
-  _LIBCPP_HIDE_FROM_ABI value_type& __get_value() {
-#    if _LIBCPP_STD_VER >= 17
-    return *std::launder(std::addressof(__cc_));
-#    else
-    return __cc_;
-#    endif
-  }
-
-  _LIBCPP_HIDE_FROM_ABI const value_type& __get_value() const {
-#    if _LIBCPP_STD_VER >= 17
-    return *std::launder(std::addressof(__cc_));
-#    else
-    return __cc_;
-#    endif
-  }
-
-  _LIBCPP_HIDE_FROM_ABI __nc_ref_pair_type __ref() {
-    value_type& __v = __get_value();
-    return __nc_ref_pair_type(const_cast<key_type&>(__v.first), __v.second);
-  }
-
-  _LIBCPP_HIDE_FROM_ABI __nc_rref_pair_type __move() {
-    value_type& __v = __get_value();
-    return __nc_rref_pair_type(std::move(const_cast<key_type&>(__v.first)), std::move(__v.second));
-  }
-
-  _LIBCPP_HIDE_FROM_ABI __value_type& operator=(const __value_type& __v) {
-    __ref() = __v.__get_value();
-    return *this;
-  }
-
-  _LIBCPP_HIDE_FROM_ABI __value_type& operator=(__value_type&& __v) {
-    __ref() = __v.__move();
-    return *this;
-  }
-
-  template <class _ValueTp, __enable_if_t<__is_same_uncvref<_ValueTp, value_type>::value, int> = 0>
-  _LIBCPP_HIDE_FROM_ABI __value_type& operator=(_ValueTp&& __v) {
-    __ref() = std::forward<_ValueTp>(__v);
-    return *this;
-  }
-
-  __value_type()                    = delete;
-  ~__value_type()                   = delete;
-  __value_type(const __value_type&) = delete;
-  __value_type(__value_type&&)      = delete;
-};
+struct _LIBCPP_STANDALONE_DEBUG __value_type;
----------------
ldionne wrote:

```suggestion
struct __value_type;
```

https://github.com/llvm/llvm-project/pull/134819