Re: c++/10394: type inference gets confused during template instantiation

["Giovanni Bajo" <giovannibajo@libero.it>]

The following reply was made to PR c++/10394; it has been noted by GNATS.

From: "Giovanni Bajo" <giovannibajo@libero.it>
To: <colby@alum.mit.edu>,
	<gcc-gnats@gcc.gnu.org>,
	<gcc-bugs@gcc.gnu.org>,
	<nobody@gcc.gnu.org>,
	<gcc-prs@gcc.gnu.org>
Cc: "Wolfgang Bangerth" <bangerth@ices.utexas.edu>
Subject: Re: c++/10394: type inference gets confused during template instantiation
Date: Mon, 14 Apr 2003 03:24:12 +0200

 http://gcc.gnu.org/cgi-bin/gnatsweb.pl?cmd=view%20audit-trail&database=gcc&p
 r=10394
 
 Your code is ill-formed, and correctly rejected by any GCC version I have
 (even if the error message could use a lifting).
 
 To invoke correctly the function, you have to use this syntax:
 
     a.f(typename A<typename V::X>::template B<int>());
 
 Because:
 
 - B<> is a nested template within A<>. A<> is dependent on C's template
 parameter, so the keyword 'template' is needed in front of it to
 disambiguate the parser.
 - The whole expression A<typename V::X>::template B<int> refers to a type
 name, which is dependent on C's template paremter, so the keyword 'typename'
 is needed in front of it to disambiguate the parser.
 
 Your line marked as [1] compiles because it is a function declaration, not
 an object instantiation. Specifically, you're declaring a function called
 "c" which returns an object of type C<E>, and accepts as parameter a pointer
 to a function which gets no parameters and returns a A<int>.
 
 Nonetheless, I found a regression on the mainline while playing with this:
 
 -------------------------------------------------------
 template <class T>
 struct A
 {
   template <class U>
   class B {};
 };
 
 template <class V>
 struct C
 {
   C()
   {
       A<typename V::X>::template B<int> k;
   }
 };
 
 struct E
 {
   typedef int X;
 };
 
 template struct C<E>;
 
 int main()
 {}
 -------------------------------------------------------
 pr10394.cpp: In constructor `C<V>::C()':
 pr10394.cpp:13: error: expected `;'
 pr10394.cpp: In constructor `C<V>::C() [with V = E]':
 pr10394.cpp:22:   instantiated from here
 pr10394.cpp:13: internal compiler error: in resolve_offset_ref, at
 cp/init.c:
    1841
 Please submit a full bug report,
 
 on 3.4 20030413. Since the code is ill-formed (missing 'typename' keyword at
 the start of the definition of k), this is a 3.4 regression,
 ice-on-illegal-code. Previous versions (2.95 -> 3.3) reports some kind of
 (unreadable) error message at least.
 
 Giovanni Bajo