http://gcc.gnu.org/bugzilla/show_bug.cgi?id=51013
Bug #: 51013
Summary: complex::{imag,real}() should maintain
lvalue-returning extension in C++11
Classification: Unclassified
Product: gcc
Version: 4.6.2
Status: UNCONFIRMED
Severity: normal
Priority: P3
Component: libstdc++
AssignedTo: unassig...@gcc.gnu.org
ReportedBy: jyass...@gcc.gnu.org
In C++98, libstdc++ has an extension to return T& from complex<T>::real() and
::imag() (introduced in r75680). Paolo removed this extension for C++11 in
r135878 citing
http://www.open-std.org/jtc1/sc22/wg21/docs/lwg-defects.html#387. However, the
point of DR387 was to increase the amount of access complex<> provides to its
internals, not to remove existing extensions providing such access.
Removing this extension affects code that passes references to the real or
imaginary parts of a complex number to other routines. While such code can
generally be rewritten in a straightforward way, it seems like an unnecessary
hurdle that should be avoided given all the other changes needed for C++11
compatibility.
The DR387-provided reinterpret_cast<> way of getting access to the addresses
would work if we were migrating to C++11 atomically, but that's impossible in a
large codebase. I believe the reinterpret_cast produces undefined behavior in
C++98 because of the aliasing violation, so we can't use it in code that needs
to be correct in both versions of the language.
So I think the extension should be reinstated.
