Bug#400332: g++-4.1: inline destructor must be defined in-class

["Frank B. Brokken" <f.b.brokken@rug.nl>]

Package: g++-4.1
Version: 4.1.1-19
Severity: normal


Dear Maintainers,

    While performing maintenance on my Bobcat library, suddenly my program
Bisonc++ FTBFS. The maintenance to Bobcat involved placing all inline member
function definitions below their class interfaces. Removing all non-essential
stuff, the full source of the stripped-down version of the program that could
not be constructed looks like this:

  class Class
  {
      public:
          virtual ~Class();
          virtual char const *what() const;
  };                                       
  
  inline Class::~Class()
  {}                    
  
  int main()
  {}

In its original version, the above program was implemented as follows:

  class Class
  {
      public:
          virtual ~Class()
          {}
          virtual char const *what() const;
  };
  
  int main()
  {}

The difference being that the former program defines its destructor below the
class body, whereas the latter program defines it inside the class body. The
error that's reported is a linker error, suggesting that the vtable must be
linked even though no use of it is implied by the program:

    /tmp/ccWzeW1i.o:(.rodata._ZTV5Class[vtable for Class]+0x10): undefined
    reference to `Class::what() const'

I found a work-around, but consider that a kludge, since it is stated in my
copy of the C++ standard (where it says *either* an inline function's
declaration *or* its definition should contain `inline'):

> 9.4 Member functions [class.mfct]
>
> An inline member function (whether static or nonstatic) may also be defined
> outside of its class definition provided either its declaration in the class
> definition or its definition outside of the class definition declares the
> function as inline (7.1.2).

So, here's my kludge, which has `inline' in *both* the class definition *and*
the implementation:

  class Class
  {
      public:
          inline virtual ~Class();
          virtual char const *what() const;
  };
  
  inline Class::~Class()
  {}                                    
  
  int main() 
  {}
  
For the sake of completeness, I also tried a version having inline specified
in the class definition but not with the destructor's definition:

  class Class
  {
      public:
          inline virtual ~Class();
          virtual char const *what() const;
  };
  
  Class::~Class()
  {}                                    
  
  int main() 
  {}
  
This last variant also compiles and links flawlessly and is conform the
standard's text. So, it looks as though `inline' currently needs to be
specified explicitly for virtual destructor declarations, or that the virtual
destructor must be given an in-class implementation. I think requiring
`inline' in the class definition is a bug.

Kind regards,

Frank Brokken.

PS: reportbug reported that g++-4.1* is now at 4.1.1-20, but upgrading still
    keeps the compiler at -19, which is also received when downloading
    explicitly from packages/debian.org, even though it reports version
    4.1.1-20 there for the i386 architectures. So, I tried all this on the -19
    version. 

-- System Information:
Debian Release: 4.0
  APT prefers testing
  APT policy: (500, 'testing')
Architecture: i386 (i686)
Shell:  /bin/sh linked to /bin/bash
Kernel: Linux 2.6.16
Locale: LANG=C, LC_CTYPE=C (charmap=ANSI_X3.4-1968)

Versions of packages g++-4.1 depends on:
ii  gcc-4.1                      4.1.1-19    The GNU C compiler
ii  gcc-4.1-base                 4.1.1-19    The GNU Compiler Collection (base 
ii  libc6                        2.3.6.ds1-8 GNU C Library: Shared libraries
ii  libstdc++6-4.1-dev           4.1.1-19    The GNU Standard C++ Library v3 (d

g++-4.1 recommends no packages.

-- no debconf information