Re: typedef of class vs class?
On 12/18/2013 7:22 PM, Ed Anson wrote:
As I read the standard (and various texts on the language) a typedef of
a class is simply a synonym for the class name. So I am surprised that
the following code fails to compile on any C++ compiler I have access to:
class bar;
template <class T>
class foo
{
public:
foo(const T& v) : m(v) {}
T m;
};
typedef foo<int> bar;
Gcc 4.6.3 gives the following error [as slightly mangled by putty]:
TypedefAnomaly.cpp:11:18: error: conflicting declaration ??typedef class
foo<int> bar??
TypedefAnomaly.cpp:1:7: error: ??struct bar?? has a previous declaration
as ??struct bar??
Other compilers claim that the forward declaration of bar is
incompatible with the typedef, but don't say why. Is there some fine
point in the C++ standard that I am missing? Must be, since it's
unlikely that all the compilers have the same bug.
In the context following the forward-declaration, 'bar' is already known
to be a 'class-name'. With 'typedef' you're reintroducing it as a
'typedef-name'. They are two different concepts in the Standard, as I
understand it, and have slightly different meanings and uses. Perhaps
this is what all the compilers are trying to tell us.
V
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