[basic.compound] - C++20 → C++23

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@@ -15,17 +15,16 @@ Compound types can be constructed in the following ways:
   a set of types, enumerations and functions for manipulating these
   objects [[class.mfct]], and a set of restrictions on the access to
   these entities [[class.access]];
 - *unions*, which are classes capable of containing objects of different
   types at different times, [[class.union]];
-- *enumerations*, which comprise a set of named constant values. Each
-  distinct enumeration constitutes a different *enumerated type*,
   [[dcl.enum]];
-- *pointers to non-static class members*, [^23] which identify members
- of a given type within objects of a given class, [[dcl.mptr]].
- Pointers to data members and pointers to member functions are
- collectively called *pointer-to-member* types.
 These methods of constructing types can be applied recursively;
 restrictions are mentioned in  [[dcl.meaning]]. Constructing a type such
 that the number of bytes in its object representation exceeds the
 maximum value representable in the type `std::size_t` [[support.types]]
@@ -56,28 +55,29 @@ allowed although there are restrictions on what can be done with them
 - the *null pointer value* for that type, or
 - an *invalid pointer value*.
 A value of a pointer type that is a pointer to or past the end of an
 object *represents the address* of the first byte in memory
-[[intro.memory]] occupied by the object [^24] or the first byte in
-memory after the end of the storage occupied by the object,
-respectively.
 [*Note 2*: A pointer past the end of an object [[expr.add]] is not
-considered to point to an unrelated object of the object’s type that
-might be located at that address. A pointer value becomes invalid when
-the storage it denotes reaches the end of its storage duration; see
-[[basic.stc]]. — *end note*]
-For purposes of pointer arithmetic [[expr.add]] and comparison (
-[[expr.rel]], [[expr.eq]]), a pointer past the end of the last element
-of an array `x` of n elements is considered to be equivalent to a
-pointer to a hypothetical array element n of `x` and an object of type
-`T` that is not an array element is considered to belong to an array
-with one element of type `T`. The value representation of pointer types
-is *implementation-defined*. Pointers to layout-compatible types shall
-have the same value representation and alignment requirements
 [[basic.align]].
 [*Note 3*: Pointers to over-aligned types [[basic.align]] have no
 special representation, but their range of valid values is restricted by
 the extended alignment requirement. — *end note*]
@@ -86,13 +86,12 @@ Two objects *a* and *b* are *pointer-interconvertible* if:
 - they are the same object, or
 - one is a union object and the other is a non-static data member of
   that object [[class.union]], or
 - one is a standard-layout class object and the other is the first
-  non-static data member of that object, or, if the object has no
- non-static data members, any base class subobject of that object
-  [[class.mem]], or
 - there exists an object *c* such that *a* and *c* are
   pointer-interconvertible, and *c* and *b* are
   pointer-interconvertible.
 If two objects are pointer-interconvertible, then they have the same
@@ -101,10 +100,15 @@ the other via a `reinterpret_cast` [[expr.reinterpret.cast]].
 [*Note 4*: An array object and its first element are not
 pointer-interconvertible, even though they have the same
 address. — *end note*]
 A pointer to cv `void` can be used to point to objects of unknown type.
 Such a pointer shall be able to hold any object pointer. An object of
-type cv `void*` shall have the same representation and alignment
-requirements as cv `char*`.

   a set of types, enumerations and functions for manipulating these
   objects [[class.mfct]], and a set of restrictions on the access to
   these entities [[class.access]];
 - *unions*, which are classes capable of containing objects of different
   types at different times, [[class.union]];
+- *enumerations*, which comprise a set of named constant values,
   [[dcl.enum]];
+- *pointers to non-static class members*,[^19] which identify members of
+  a given type within objects of a given class, [[dcl.mptr]]. Pointers
+  to data members and pointers to member functions are collectively
+  called *pointer-to-member* types.
 These methods of constructing types can be applied recursively;
 restrictions are mentioned in  [[dcl.meaning]]. Constructing a type such
 that the number of bytes in its object representation exceeds the
 maximum value representable in the type `std::size_t` [[support.types]]
 - the *null pointer value* for that type, or
 - an *invalid pointer value*.
 A value of a pointer type that is a pointer to or past the end of an
 object *represents the address* of the first byte in memory
+[[intro.memory]] occupied by the object[^20]
+or the first byte in memory after the end of the storage occupied by the
+object, respectively.
 [*Note 2*: A pointer past the end of an object [[expr.add]] is not
+considered to point to an unrelated object of the object’s type, even if
+the unrelated object is located at that address. A pointer value becomes
+invalid when the storage it denotes reaches the end of its storage
+duration; see [[basic.stc]]. — *end note*]
+For purposes of pointer arithmetic [[expr.add]] and comparison
+[[expr.rel]], [[expr.eq]], a pointer past the end of the last element of
+an array `x` of n elements is considered to be equivalent to a pointer
+to a hypothetical array element n of `x` and an object of type `T` that
+is not an array element is considered to belong to an array with one
+element of type `T`. The value representation of pointer types is
+*implementation-defined*. Pointers to layout-compatible types shall have
+the same value representation and alignment requirements
 [[basic.align]].
 [*Note 3*: Pointers to over-aligned types [[basic.align]] have no
 special representation, but their range of valid values is restricted by
 the extended alignment requirement. — *end note*]
 - they are the same object, or
 - one is a union object and the other is a non-static data member of
   that object [[class.union]], or
 - one is a standard-layout class object and the other is the first
+  non-static data member of that object or any base class subobject of
+ that object [[class.mem]], or
 - there exists an object *c* such that *a* and *c* are
   pointer-interconvertible, and *c* and *b* are
   pointer-interconvertible.
 If two objects are pointer-interconvertible, then they have the same
 [*Note 4*: An array object and its first element are not
 pointer-interconvertible, even though they have the same
 address. — *end note*]
+A byte of storage *b* is *reachable through* a pointer value that points
+to an object *x* if there is an object *y*, pointer-interconvertible
+with *x*, such that *b* is within the storage occupied by *y*, or the
+immediately-enclosing array object if *y* is an array element.
 A pointer to cv `void` can be used to point to objects of unknown type.
 Such a pointer shall be able to hold any object pointer. An object of
+type “pointer to cv `void`” shall have the same representation and
+alignment requirements as an object of type “pointer to cv `char`”.

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