[Bug c++/41690] New: Scoping is incorrect for inherited classes nested inside a templated class.

[Bug c++/41690] New: Scoping is incorrect for inherited classes nested inside a templated class.

[timothy dot renner at gmail dot com]

When a nested class inherits from another nested class, scoping is incorrect
only if the outer class is templated.  A full .ii file follows, but to
illustrate in a compact example:

class A {
  class B {
    protected:
      int d_data;
  };
  class C : public B {
    void foo() { d_data = 0; }
  };
};

If A is *not* templated, the code will compile.  If A is templated, the
compiler complains that d_data has not been declared in the current scope.


There is no option for attaching files, so the .ii file follows:
--------------------------%<----------------------------------------

# 1 "a.cpp"
# 1 "<built-in>"
# 1 "<command-line>"
# 1 "a.cpp"
# 1 "templ.h" 1
class notempl {
private:
 int d_stuff;

 class A {
 protected:
  int d_data;
 };

 class B : public A {
  void test() {
   d_data = 0;
  }
 };

};


template <class TYPE>
class templ {
private:
 int d_stuff;

 class A {
 protected:
  int d_data;
 };

 class B : public A {
  void test() {
   d_data = 0;
  }
 };

};
# 2 "a.cpp" 2

int main() {
 notempl tmp1;
 templ<int> tmp2;

 return 0;
}

--------------------------%<----------------------------------------

Detailed compilation follows:

~/tmp/gcc-bug# g++ -v -save-temps a.cpp
Using built-in specs.
Target: x86_64-linux-gnu
Configured with: ../src/configure -v --with-pkgversion='Ubuntu 4.3.3-5ubuntu4'
--with-bugurl=file:///usr/share/doc/gcc-4.3/README.Bugs
--enable-languages=c,c++,fortran,objc,obj-c++ --prefix=/usr --enable-shared
--with-system-zlib --libexecdir=/usr/lib --without-included-gettext
--enable-threads=posix --enable-nls --with-gxx-include-dir=/usr/include/c++/4.3
--program-suffix=-4.3 --enable-clocale=gnu --enable-libstdcxx-debug
--enable-objc-gc --enable-mpfr --with-tune=generic --enable-checking=release
--build=x86_64-linux-gnu --host=x86_64-linux-gnu --target=x86_64-linux-gnu
Thread model: posix
gcc version 4.3.3 (Ubuntu 4.3.3-5ubuntu4) 
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
 /usr/lib/gcc/x86_64-linux-gnu/4.3.3/cc1plus -E -quiet -v -D_GNU_SOURCE a.cpp
-D_FORTIFY_SOURCE=2 -mtune=generic -fpch-preprocess -o a.ii
ignoring nonexistent directory "/usr/local/include/x86_64-linux-gnu"
ignoring nonexistent directory
"/usr/lib/gcc/x86_64-linux-gnu/4.3.3/../../../../x86_64-linux-gnu/include"
ignoring nonexistent directory "/usr/include/x86_64-linux-gnu"
#include "..." search starts here:
#include <...> search starts here:
 /usr/include/c++/4.3
 /usr/include/c++/4.3/x86_64-linux-gnu
 /usr/include/c++/4.3/backward
 /usr/local/include
 /usr/lib/gcc/x86_64-linux-gnu/4.3.3/include
 /usr/lib/gcc/x86_64-linux-gnu/4.3.3/include-fixed
 /usr/include
End of search list.
COLLECT_GCC_OPTIONS='-v' '-save-temps' '-shared-libgcc' '-mtune=generic'
 /usr/lib/gcc/x86_64-linux-gnu/4.3.3/cc1plus -fpreprocessed a.ii -quiet
-dumpbase a.cpp -mtune=generic -auxbase a -version -fstack-protector -o a.s
GNU C++ (Ubuntu 4.3.3-5ubuntu4) version 4.3.3 (x86_64-linux-gnu)
        compiled by GNU C version 4.3.3, GMP version 4.2.4, MPFR version 2.4.0.
GGC heuristics: --param ggc-min-expand=97 --param ggc-min-heapsize=126404
Compiler executable checksum: d9dd67dcc191271ac69fd2c05266cf9c
In file included from a.cpp:2:
templ.h: In member function void templ<TYPE>::B::test():
templ.h:31: error: d_data was not declared in this scope


-- 
           Summary: Scoping is incorrect for inherited classes nested inside
                    a templated class.
           Product: gcc
           Version: 4.3.3
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: timothy dot renner at gmail dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41690

[Bug c++/41690] Scoping is incorrect for inherited classes nested inside a templated class.

[paolo dot carlini at oracle dot com]

------- Comment #1 from paolo dot carlini at oracle dot com  2009-10-13 01:08 -------
Not a bug, use this->d_data.


-- 

paolo dot carlini at oracle dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|UNCONFIRMED                 |RESOLVED
         Resolution|                            |INVALID


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41690

[Bug c++/41690] Scoping is incorrect for inherited classes nested inside a templated class.

[timothy dot renner at gmail dot com]

------- Comment #2 from timothy dot renner at gmail dot com  2009-10-13 05:47 -------
Thank you, I found that I could access it that way, and it makes a good
workaround.  I'm curious why this is not a scoping bug though?  It seems like
the compiler should still be able to scope d_data from the parent class,
especially as it works when the parent class is not templated.  If that's not
true, could you please explain it to me?  I'd like to understand this.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41690

[Bug c++/41690] Scoping is incorrect for inherited classes nested inside a templated class.

[pinskia at gcc dot gnu dot org]

------- Comment #3 from pinskia at gcc dot gnu dot org  2009-10-13 05:56 -------
>the parent class is not templated. 
Actually it is.

The name of the parent class really is templ<T>::A, which is a templated class.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41690

[Bug c++/41690] Scoping is incorrect for inherited classes nested inside a templated class.

[timothy dot renner at gmail dot com]

------- Comment #4 from timothy dot renner at gmail dot com  2009-10-13 06:38 -------
>Actually it is.
>
>The name of the parent class really is templ<T>::A, which is a templated class.

Sorry, my mistake, I mistyped that.  Let me clarify.  I didn't mean the parent
class, I meant the containing class. I'm not sure what the technical name is
for the class that houses a nested class.  Classes A and B nested in class
templ<TYPE> are definitely templated, but what about classes A and B nested in
class notempl?

What I am curious about is that the compiler does recognize inheritance in a
templated class:
If I added public constructors to both A and B:
   A() {}
and
   B() : A() {}

A() is accessibile by class B, and that code will compile, but the compiler
does not recognize that d_data from A is accessible by B when templation is
involved, but does recognize it when templation is not involved.

I can see it being a more complicated case to parse correctly, but the current
behavior seems inconsistent to me and like something the compiler should not
throw an error on, so if there is a good reason why it should work the way it
currently does, I'd really like to learn what it is.  If not, this bug should
be reopened and kept around at the very least as a "nice to have" feature since
it's easily worked around, or just flat out marked as a won't fix.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41690

[Bug c++/41690] Scoping is incorrect for inherited classes nested inside a templated class.

[paolo dot carlini at oracle dot com]

------- Comment #5 from paolo dot carlini at oracle dot com  2009-10-13 10:26 -------
To be clear, the use of this-> isn't a "workaround", is the way C++ as
specified in the current International standard works. This is not the place
for general explanations, you may want to browse D. Vandevoorde and Nicolai M.
Josuttis, "C++ Templates", Addison Wesley, for a clear treatment of the this->,
typename, ::templte, .template, etc., subtleties and *much* more.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41690

[Bug c++/41690] Scoping is incorrect for inherited classes nested inside a templated class.

[redi at gcc dot gnu dot org]

------- Comment #6 from redi at gcc dot gnu dot org  2009-10-13 11:02 -------
Or see http://gcc.gnu.org/gcc-3.4/changes.html#cplusplus


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41690

[Bug c++/41690] Scoping is incorrect for inherited classes nested inside a templated class.

[paolo dot carlini at oracle dot com]

------- Comment #7 from paolo dot carlini at oracle dot com  2009-10-13 11:55 -------
Yes, Jon. By the way, I also wanted to link to that *very* old changes doc,
probably gave up only because the examples are slightly different. But indeed,
that's exactly the point.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=41690