------- Comment #5 from walton at seas dot harvard dot edu 2010-07-21 16:35
-------
Subject: Re: Name of member class of template class cannot
be used as argument type.
OK, adding `typename::' fixed the problem with the compiler
balking at the template function definition, but now
the compiler accepts the definition and then appears
to forget it, so it cannot be used. Test code below:
see first commented line.
Is there some further syntactic magic required, or is
this a bug? If the latter, I could not find it via
search, so do you know offhand if its been reported?
Bob
PS: I also figured out a workaround for my case, but
would rather not use it if there were a more proper fix.
PPS: Sorry about the first bug report, as I figured out
the typename stuff several years ago and then forgot about
it and forward reference of specializations, etc.,
figuring I'd never want to get entangled in such. Its
clear there is no easy answer short of redesigning
C++ templates to make delayed parsing the default
and using something like <|...|> brackets instead of
<...> to avoid ambiguities with scanning a delayed
parse expression. Grumble.
Test Code
---- ----
# include <iostream>
using namespace std;
template < typename T >
class B
{
public:
class C;
};
template < typename T >
class B<T>::C { int i; };
// The following definition is accepted BUT then
// appears to be `forgotten' so it cannot be used.
//
template < typename T >
int funcC ( typename::B<T>::C * c ) { return 0; }
// Inclusion of the following makes no difference in
// the complier error message.
//
template int funcC<int> ( B<int>::C * c);
// Check that non-member class works.
//
template < typename T >
int funcB ( B<T> * b ) { return 0; }
// Check that the non-template version works.
//
class F
{
public:
class G;
};
class F::G { int j; };
void funcG ( F::G * g );
// Workaround for my case.
template < typename T >
class C2 { int k; };
template < typename T >
class B2
{
public:
typedef C2<T> C;
};
template < typename T >
int funcC2 ( C2<T> * c ) { return 0; }
int main ()
{
B<int>::C x; // OK
funcC ( & x ); // COMPILER ERROR! [line 57]
F::G y; // OK
funcG ( & y ); // OK
B<int> z; // OK
funcB ( & z ); // OK
B2<int>::C w; // OK
funcC2 ( & w ); // OK
}
Compiler Output
---------------
template-member-class-function-bug.cc: In function ¡int main()¢:
template-member-class-function-bug.cc:57: error: no matching function for call
to ¡funcC(B<int>::C*)¢
Compiler Version
-------- -------
g++ (GCC) 4.1.2 20080704 (Red Hat 4.1.2-48)
Copyright (C) 2006 Free Software Foundation, Inc.
This is free software; see the source for copying conditions. There is NO
warranty; not even for MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.
--
http://gcc.gnu.org/bugzilla/show_bug.cgi?id=45002
