On 16 Feb 2011, at 12:35, Mathias Gaunard wrote:
On 15/02/2011 21:54, Christopher Jefferson wrote:
libc++ does not allow forward declarations of types for std:: , as it uses inline namespace to allow versioning.
Is that legal?
I think so. I believe it is impossible to tell, except when trying to do forward declarations of C++ standard library types. The question is then if forward declarations of types in std:: are allowed. From 17.6.3.2.1p1 in the current C++0x draft (there is identical text in the c++03 standard): "The behavior of a C++ program is undefined if it adds declarations or definitions to namespace std or to a namespace within namespace std unless otherwise specified." While people could read this in various ways, I would say it forbids these kinds of games, although they might work for particular standard libraries.