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From: Simon MARTIN <simartin@users.sourceforge.net>
To: gcc@gcc.gnu.org
Subject: Type problem with template functions and inheritance ?
Date: Wed, 08 Sep 2004 20:10:00 -0000
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Hello.

I played a little with templates and template functions, and I encountered a 
problem with GCC while doing so. The code at the end of this message builds 
with Microsoft's Visual C++ Toolkit 2003, but fails with GCC. Since the code 
is quite "weird", I wonder whether there's a problem in GCC or Visual is too 
laxist.

What is strange is:
  - the "<unknown type>" in the error message
  - the fact that if I "help" GCC a little (before the first static_cast), 
then things work fine.

Thanks in advance for your help / explanation.

Regards,
Simon

[simon@texel gcc_test]$ g++ -v
Reading specs from /usr/lib/gcc-lib/i586-mandrake-linux-gnu/3.3.2/specs
Configured with: ../configure --prefix=/usr --libdir=/usr/lib 
--with-slibdir=/lib --mandir=/usr/share/man --infodir=/usr/share/info 
--enable-shared --enable-threads=posix --disable-checking --enable-long-long 
--enable-__cxa_atexit --enable-clocale=gnu 
--enable-languages=c,c++,ada,f77,objc,java,pascal 
--host=i586-mandrake-linux-gnu --with-system-zlib
Thread model: posix
gcc version 3.3.2 (Mandrake Linux 10.0 3.3.2-6mdk)

[simon@texel gcc_test]$ g++ -Wall -o test test.cpp
test.cpp: In function `int main(int, char**)':
test.cpp:18: error: invalid static_cast from type `<unknown type>' to type 
`bool (Base::*)(const char*)'

==== test.cpp
class Base {};
struct MyClass : public Base
{
  template<int key> bool Method(const char *value) { return true; }
};

int main(int argc, char *argv[])
{
  typedef bool (Base::*BaseMethodPtr)(const char*);
  typedef bool (MyClass::*MethodPtr)(const char*);

  MyClass aClass;

  MethodPtr mp = &MyClass::Method<1>;
  BaseMethodPtr p1 = static_cast<BaseMethodPtr>(mp);
  (aClass.*p1)("One");

  BaseMethodPtr p2 = static_cast<BaseMethodPtr>(&MyClass::Method<1>);
  (aClass.*p2)("OneAgain");

  return 0;
}
==== end of test.cpp

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