[basic.stc.dynamic.safety] - C++20 → C++23

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-##### Safely-derived pointers <a id="basic.stc.dynamic.safety">[[basic.stc.dynamic.safety]]</a>
-A *traceable pointer object* is
-- an object of an object pointer type [[basic.compound]], or
-- an object of an integral type that is at least as large as
-  `std::intptr_t`, or
-- a sequence of elements in an array of narrow character type
-  [[basic.fundamental]], where the size and alignment of the sequence
-  match those of some object pointer type.
-A pointer value is a *safely-derived pointer* to an object with dynamic
-storage duration only if the pointer value has an object pointer type
-and is one of the following:
-- the value returned by a call to the C++ standard library
-  implementation of `::operator new(std::{}size_t)` or
-  `::operator new(std::size_t, std::align_val_t)` ;[^16]
-- the result of taking the address of an object (or one of its
-  subobjects) designated by an lvalue resulting from indirection through
-  a safely-derived pointer value;
-- the result of well-defined pointer arithmetic [[expr.add]] using a
-  safely-derived pointer value;
-- the result of a well-defined pointer conversion ([[conv.ptr]],
-  [[expr.type.conv]], [[expr.static.cast]], [[expr.cast]]) of a
-  safely-derived pointer value;
-- the result of a `reinterpret_cast` of a safely-derived pointer value;
-- the result of a `reinterpret_cast` of an integer representation of a
-  safely-derived pointer value;
-- the value of an object whose value was copied from a traceable pointer
-  object, where at the time of the copy the source object contained a
-  copy of a safely-derived pointer value.
-An integer value is an *integer representation of a safely-derived
-pointer* only if its type is at least as large as `std::intptr_t` and it
-is one of the following:
-- the result of a `reinterpret_cast` of a safely-derived pointer value;
-- the result of a valid conversion of an integer representation of a
-  safely-derived pointer value;
-- the value of an object whose value was copied from a traceable pointer
-  object, where at the time of the copy the source object contained an
-  integer representation of a safely-derived pointer value;
-- the result of an additive or bitwise operation, one of whose operands
-  is an integer representation of a safely-derived pointer value `P`, if
-  that result converted by `reinterpret_cast<void*>` would compare equal
-  to a safely-derived pointer computable from
-  `reinterpret_cast<void*>(P)`.
-An implementation may have *relaxed pointer safety*, in which case the
-validity of a pointer value does not depend on whether it is a
-safely-derived pointer value. Alternatively, an implementation may have
-*strict pointer safety*, in which case a pointer value referring to an
-object with dynamic storage duration that is not a safely-derived
-pointer value is an invalid pointer value unless the referenced complete
-object has previously been declared reachable [[util.dynamic.safety]].
-[*Note 6*: The effect of using an invalid pointer value (including
-passing it to a deallocation function) is undefined, see  [[basic.stc]].
-This is true even if the unsafely-derived pointer value might compare
-equal to some safely-derived pointer value. — *end note*]
-It is *implementation-defined* whether an implementation has relaxed or
-strict pointer safety.

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