https://gcc.gnu.org/bugzilla/show_bug.cgi?id=97432
--- Comment #1 from Ray Zhang <peifeng2005 at gmail dot com> ---
Providing more context with the first example (also applies for the rest):
1) // pointer to array - works in clang (trunk),
// works in gcc (trunk)
reinterpret_cast<int* const T::* const (*) [2]>(x);
T1: const pointer to const pointer to const pm(T) to const pointer to const U1
T2: pointer to const array of 2 const pm(T) to const pointer to U2
In this case, there exists multiple cv-decompositions, as [7.3.6].1 example 1
states:
> [Example 1: The type denoted by the type-id const int ** has three
> cv-decompositions, taking U as “int”, as “pointer to const int”, and as
> “pointer to pointer to const int”.
The cv-decompositions we have here for T1 is:
- const pointer to const U1
- const pointer to const pointer to const U1
- const pointer to const pointer to const pm(T) to const U1
- const pointer to const pointer to const pm(T) to const pointer to const U1
If we fulfill one such cv-decompositions, we can consider that reinterpret_cast
will not cast away constness, though U1 and U2 may be nested pointer/array
types of interest.
The unique cv-decomposition that a compiler can decide to take of T1 is:
- const pointer to const U1, where U1 is "pointer to const pm(T) to const
pointer to const int"
The cv-decomposition on T2 can be done similarly:
- const pointer to const U2, where U2 is "array of 2 const pm(T) to const
pointer to int"
Thus, we can perform a reinterpret cast from U1 to U2 without casting away
constness.
