[Bug c++/11828] [3.4/4.0 regression] qualified dependent name looked up too early

[Bug c++/11828] [3.4/4.0 regression] qualified dependent name looked up too early

[pinskia at gcc dot gnu dot org]

------- Comment #23 from pinskia at gcc dot gnu dot org  2006-02-07 02:24 -------
*** Bug 26148 has been marked as a duplicate of this bug. ***


-- 

pinskia at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |gcc_bugzilla at friedman dot
                   |                            |to


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11828

[Bug c++/11828] [3.4/4.0 regression] qualified dependent name looked up too early

[pinskia at gcc dot gnu dot org]

------- Comment #24 from pinskia at gcc dot gnu dot org  2006-02-08 17:44 -------
*** Bug 26148 has been marked as a duplicate of this bug. ***


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11828

[Bug c++/11828] New: [3.4 regression] qualified dependent name looked up too early

[benko at sztaki dot hu]

PLEASE REPLY TO gcc-bugzilla@gcc.gnu.org ONLY, *NOT* gcc-bugs@gcc.gnu.org.

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11828

           Summary: [3.4 regression] qualified dependent name looked up too
                    early
           Product: gcc
           Version: 3.4
            Status: UNCONFIRMED
          Severity: normal
          Priority: P2
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: benko at sztaki dot hu
                CC: gcc-bugs at gcc dot gnu dot org

hydra:~/c/proba$ cat templ_overload.cc
namespace n
{
  template <typename T>
  void
  f(T a)
  {
    a.f();
  }

  template <typename T>
  void
  g(T a)
  {
    n::f(a);
  }
}

struct s
{};

namespace n
{
  void
  f(s)
  {}
}

int
main()
{
  n::g(s());

  return 0;
}
hydra:~/c/proba$ g++-cvs templ_overload.cc
templ_overload.cc: In function `void n::f(T) [with T = s]':
templ_overload.cc:14:   instantiated from `void n::g(T) [with T = s]'
templ_overload.cc:31:   instantiated from here
templ_overload.cc:7: error: 'struct s' has no member named 'f'
zsh: exit 1     g++-cvs templ_overload.cc
hydra:~/c/proba$ g++-cvs -v
Reading specs from /gml/shared/gcc-cvs/lib/gcc/i686-pc-linux-gnu/3.4/specs
Configured with: ../gcc/configure --prefix=/gml/shared/gcc-cvs
--enable-languages=c++
Thread model: posix
gcc version 3.4 20030806 (experimental)
hydra:~/c/proba$ g++3 templ_overload.cc
hydra:~/c/proba$ g++3 -v
Reading specs from /gml/shared/gcc-3.3/lib/gcc-lib/i686-pc-linux-gnu/3.3/specs
Configured with: ../gcc-3.3/configure --prefix=/gml/shared/gcc-3.3
Thread model: posix
gcc version 3.3
hydra:~/c/proba$ 

workarounds:
1. unqualify f in the definition of g.
   I cannot do this, because in real life n=std, f=iter_swap, g=reverse.
2. Move the definition of the overload for f before the definition of g.

[Bug c++/11828] [3.4/4.0 regression] qualified dependent name looked up too early

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2004-10-28 13:53 -------
*** Bug 18195 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |schepler at math dot
                   |                            |berkeley dot edu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11828

[Bug c++/11828] [3.4/4.0 regression] qualified dependent name looked up too early

[smcpeak at cs dot berkeley dot edu]

------- Additional Comments From smcpeak at cs dot berkeley dot edu  2005-02-21 02:41 -------
I question the apparent conclusion reached in this discussion.  The
reporter's testcase refers to

  n::f(a)

where 'a' has dependent type.

The conclusion so far is that 'f' is not dependent because it is
qualified.  The primary justification offered is that 14.6.2p1
mentions exactly two syntactic cases of dependent names:

  - function call with a simple 'identifier' as the function
  - operator in an expression

However, as discussed here and elsewhere
(e.g., http://gcc.gnu.org/onlinedocs/gcc/Name-lookup.html),
there is general consensus that the following forms also make
'f' dependent:

  - x->f(a)          // when x is a type-dependent expression
  - C::f(a)          // when C is a dependent type

Therefore, my interpretation is that the two cases given in 14.6.2 are
*not* exhaustive, but rather merely examples.  14.6.2 first gives some
general properties of dependent names (e.g., "... semantics which may
differ from one instantiation to another.") that clearly apply to more
situations.  And 14.6.4.2 singles out unqualified names as a special
case---why would they be a special case if only unqualified names
could be dependent?

Now, it is true that the two additional generally-agreed-upon cases
above are "doubly" dependent: not only do they have arguments of
dependent type, but their receiver object or qualifier is also of
dependent type.  Consequently, the expressions are type-dependent
(14.6.2.2 p1, p3 resp.); but the standard never says that being part
of a type-dependent expression automatically makes the name dependent!
On the contrary, 14.6.2.2p4 gives several counterexamples.  Moreover,
in the simple case "f(a)", 'f' is not a type-dependent expression, and
yet it is clearly a dependent name.

Extrapolating from the first few sentences of 14.6.2, it seems to me
that the following are exhaustive representatives of cases where the
name 'foo' is dependent:

A.  Cases where function overload resolution is performed, and
influenced by some type that might be dependent:

  A1. foo(a,b,c)
  A2. C::foo(a,b,c)
  A3. x->foo(a,b,c)
  A4. x->C::foo(a,b,c)

when a or b or c is a type-dependent expression.

B.  Cases where lookup involves traversing a class with dependent
type:

  B1. C::foo
  B2. x->foo
  B3. x->C::foo

when C is a dependent type, or x is a type-dependent expression.

C.  Cases when the address of an overloaded function is matched to a
target type (13.4) that is dependent.  This would include all
variations of

  C.  [&][x->][C::]foo

where by brackets ([]) I mean optional component.

In all cases (except case C, I *think*) 'foo' could be a template-id,
and would still be dependent.  (Plus the case of operators in
expressions where an operand is a type-dependent expr.)


-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |smcpeak at cs dot berkeley
                   |                            |dot edu


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11828

[Bug c++/11828] [3.4/4.0 regression] qualified dependent name looked up too early

[pinskia at gcc dot gnu dot org]

------- Additional Comments From pinskia at gcc dot gnu dot org  2005-03-03 22:55 -------
*** Bug 20307 has been marked as a duplicate of this bug. ***

-- 
           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |vasilche at ncbi dot nlm dot
                   |                            |nih dot gov


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11828

[Bug c++/11828] [3.4/4.0 regression] qualified dependent name looked up too early

[smcpeak at cs dot berkeley dot edu]

------- Additional Comments From smcpeak at cs dot berkeley dot edu  2005-03-04 05:00 -------
I think I have answered my own question: indeed, qualified lookup
only considers name from the definition context, and not the
instantiation context.

I found this thread at google groups:

 
http://groups-beta.google.com/group/comp.std.c++/browse_thread/thread/22521f9b57b995d0/73d79aadca8c665c

Quoting from a few of the more useful messages:

  http://groups-beta.google.com/group/comp.std.c++/msg/ae689cfc9c99262d

    Moving to templates. Point of definition does both normal and argument
    dependent lookup, point of instantiation does ADL only (14.6.4/1.)

    When you disable ADL by writing N::foo(x), the only lookup that
    remains is normal lookup done at point of definition. Point of
    instantiation lookup is implicitly disabled as a consequence of the
    interaction between 3.4.2/1 and 14.6.4/1.

  http://groups-beta.google.com/group/comp.std.c++/msg/0e252a95da0f453d

    The OL
    part happens at the point of definition (phase 1), and  the ADL
    part happens at the POI (point of instantiation; phase 2).  If
    you remove the ADL part, you're left with a phase 1 lookup only.

  http://groups-beta.google.com/group/comp.std.c++/msg/6a53b35efe39fee3

    The compromise that was reached was to say that lexical lookup
    would occur only in the definition context; only ADL would be
    performed in the instantiation context.  Since qualified
    function names do not participate in ADL, any arguments in a
    call to a qualified name are ignored in determining whether a
    qualified name is dependent or not.

The upshot is that, by 14.6.4p1, second-phase lookup *only* does
argument-dependent lookup, which is itself disabled by qualification.

This has some nasty consequences, e.g.

  http://groups-beta.google.com/group/comp.std.c++/msg/8379998d36b27a99

but appears to be the genuine intent of the committee.


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http://gcc.gnu.org/bugzilla/show_bug.cgi?id=11828