RE: Error on GCC 3.4 release web page

RE: Error on GCC 3.4 release web page

[Johan Bergman (KI/EAB)]

Hi again,

Maybe you could also mention the following alternative corrected definition of C<T>::h.
It might save a lot of work for those struggling to make their code GCC 3.4 compliant.

	template <typename T> struct C : B<T> {
	  using B<T>::m;
	  using B<T>::f;
	  using B<T>::n;
	  using B<T>::g;
	  void h ()
	  {
	    m = 0;
	    f ();
	    n = 0;
	    g ();
	  }
	};

BR,
Johan


-----Original Message-----
From: Johan Bergman (KI/EAB) 
Sent: den 18 september 2004 00:07
To: 'gcc@gnu.org'
Subject: Error on GCC 3.4 release web page


Hi,

There seems to be an error in the following example, found on http://gcc.gnu.org/gcc-3.4/changes.html.

  In a template definition, unqualified names will no longer find members of a dependent base. For example,
 
      template <typename T> struct B {
	  int m;
	  int n;
	  int f ();
	  int g ();
	};
	int n;
	int g ();
	template <typename T> struct C : B<T> {
	  void g ()
	  {
	    m = 0; // error
	    f ();  // error
	    n = 0; // ::n is modified
	    g ();  // ::g is called
	  }
	};

  You must make the names dependent by prefixing them with this->. Here is the corrected definition of C<T>::g,

	template <typename T> void C<T>::g ()
	{
	  this->m = 0;
	  this->f ();
	  this->n = 0
	  this->g ();
	}

The problem with the example is that the member function g() in C<T> calls itself. The following should work better:

  In a template definition, unqualified names will no longer find members of a dependent base. For example,

      template <typename T> struct B {
	  int m;
	  int n;
	  int f ();
	  int g ();
	};
	int n;
	int g ();
	template <typename T> struct C : B<T> {
	  void h ()
	  {
	    m = 0; // error
	    f ();  // error
	    n = 0; // ::n is modified
	    g ();  // ::g is called
	  }
	};

  You must make the names dependent by prefixing them with this->. Here is the corrected definition of C<T>::h,

	template <typename T> void C<T>::h ()
	{
	  this->m = 0;
	  this->f ();
	  this->n = 0
	  this->g ();
	}

My only change was that 'g' was replaced with 'h' in three places (two in the code and one in the text).

BR,
Johan

Re: Error on GCC 3.4 release web page

[Giovanni Bajo]

Johan Bergman (KI/EAB) wrote:

> There seems to be an error in the following example, found on
http://gcc.gnu.org/gcc-3.4/changes.html.
> The problem with the example is that the member function g() in C<T> calls
itself.

Actually the example is meant to show name lookup issue, not to have a proper
runtime behaviour. Anyway, I would not object renaming that function to avoid
any confusion for the user.

> Maybe you could also mention the following alternative corrected
> definition of C<T>::h.

> template <typename T> struct C : B<T> {
>   using B<T>::m;
>   using B<T>::f;
>   using B<T>::n;
>   using B<T>::g;

Makes sense. Can you please provide a patch against the HTML file, and post it
to gcc-patches@gcc.gnu.org?

Thanks,
Giovanni Bajo

Error on GCC 3.4 release web page

[Johan Bergman (KI/EAB)]

Hi,

There seems to be an error in the following example, found on http://gcc.gnu.org/gcc-3.4/changes.html.

  In a template definition, unqualified names will no longer find members of a dependent base. For example,
 
      template <typename T> struct B {
	  int m;
	  int n;
	  int f ();
	  int g ();
	};
	int n;
	int g ();
	template <typename T> struct C : B<T> {
	  void g ()
	  {
	    m = 0; // error
	    f ();  // error
	    n = 0; // ::n is modified
	    g ();  // ::g is called
	  }
	};

  You must make the names dependent by prefixing them with this->. Here is the corrected definition of C<T>::g,

	template <typename T> void C<T>::g ()
	{
	  this->m = 0;
	  this->f ();
	  this->n = 0
	  this->g ();
	}

The problem with the example is that the member function g() in C<T> calls itself. The following should work better:

  In a template definition, unqualified names will no longer find members of a dependent base. For example,

      template <typename T> struct B {
	  int m;
	  int n;
	  int f ();
	  int g ();
	};
	int n;
	int g ();
	template <typename T> struct C : B<T> {
	  void h ()
	  {
	    m = 0; // error
	    f ();  // error
	    n = 0; // ::n is modified
	    g ();  // ::g is called
	  }
	};

  You must make the names dependent by prefixing them with this->. Here is the corrected definition of C<T>::h,

	template <typename T> void C<T>::h ()
	{
	  this->m = 0;
	  this->f ();
	  this->n = 0
	  this->g ();
	}

My only change was that 'g' was replaced with 'h' in three places (two in the code and one in the text).

BR,
Johan