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From: "daniel.kruegler at googlemail dot com" <gcc-bugzilla@gcc.gnu.org>
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Subject: [Bug c++/49171] [C++0x][constexpr] Constant expressions support reinterpret_cast
Date: Tue, 30 Aug 2011 09:52:00 -0000
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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=3D49171

--- Comment #2 from Daniel Kr=C3=BCgler <daniel.kruegler at googlemail dot =
com> 2011-08-30 09:39:43 UTC ---
I believe I found a conforming usage of reinterpret_cast in constant
expressions useable in C++03:

//----------------
struct X {
 X* operator&();
};

X x[2];

const bool p =3D (reinterpret_cast<X*>(&reinterpret_cast<char&>(x[1]))
- reinterpret_cast<X*>(&reinterpret_cast<char&>(x[0]))) =3D=3D sizeof(X);

enum E { e =3D p }; // e should have a value equal to 1
//----------------

Basically this program demonstrates the technique, the C++11 library functi=
on
addressof is based on and thus excluding reinterpret_cast *unconditionally*
from constant expressions in the core language would render this useful pro=
gram
invalid and would make it impossible to declare addressof as a constexpr
function.