[Bug c++/31423] New: Improve upon "invalid use of member (did you forget the '&' ?)"

[Bug c++/31423] New: Improve upon "invalid use of member (did you forget the '&' ?)"

[gerald at pfeifer dot com]

For the program

   struct C {
     int f() { return 1; }
   };

   int f(C &c) {
     return ( 1 == c.f );
   }

we currently issue

   In function 'int f(C&)':
   6: error: invalid use of member (did you forget the '&' ?)

Basically, my thought is that whenever we encounter a comparison of a
member function c.f with a value that is compatible with its return type,
the author of the code probably ment to write c.f() instead of &c.f, so
the error message could propose the former.

Specifically, I suggest to issue
  error: invalid use of member (did you forget the "()" ?)
instead of
  error: invalid use of member (did you forget the '&' ?)
when the return type of the function c.f is an integer type and we
compare against an integer constant as per my original example.


-- 
           Summary: Improve upon "invalid use of member (did you forget the
                    '&' ?)"
           Product: gcc
           Version: 4.3.0
            Status: UNCONFIRMED
          Severity: normal
          Priority: P3
         Component: c++
        AssignedTo: unassigned at gcc dot gnu dot org
        ReportedBy: gerald at pfeifer dot com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[bangerth at dealii dot org]

------- Comment #1 from bangerth at dealii dot org  2007-04-02 17:09 -------
Confirmed.
W.


-- 

bangerth at dealii dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |bangerth at dealii dot org
             Status|UNCONFIRMED                 |NEW
     Ever Confirmed|0                           |1
   Last reconfirmed|0000-00-00 00:00:00         |2007-04-02 17:09:15
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[manu at gcc dot gnu dot org]

------- Comment #2 from manu at gcc dot gnu dot org  2009-08-05 15:33 -------
Perhaps we could just mention both '&' and '()'? It seems a bit difficult to
check all the conditions that you mention.

BTW, shouldn't it say 'member function'? Can this be anything different than a
member function?


-- 

manu at gcc dot gnu dot org changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
   Last reconfirmed|2007-04-02 17:09:15         |2009-08-05 15:33:05
               date|                            |


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[jwakely dot gcc at gmail dot com]

------- Comment #3 from jwakely dot gcc at gmail dot com  2009-08-05 16:40 -------
&c.f isn't even valid, it should be &C::f

I didn't check the code, but that message isn't used for member variables or
nested types, so if it does only apply to member functions then I think
changing '&' to '()' unconditionally makes sense.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[bangerth at gmail dot com]

------- Comment #4 from bangerth at gmail dot com  2009-08-05 17:54 -------
(In reply to comment #3)
> &c.f isn't even valid, it should be &C::f
> 
> I didn't check the code, but that message isn't used for member variables or
> nested types, so if it does only apply to member functions then I think
> changing '&' to '()' unconditionally makes sense.

It also strictly wouldn't make things worse: the message we currently print
hardly ever has anything to do with what is really happening, and replacing
the ampersand by parentheses can only make things better even if it isn't
always correct.

W.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[bangerth at gmail dot com]

------- Comment #5 from bangerth at gmail dot com  2009-08-05 17:57 -------
However, one of my gripes with the previous error message is that it's
just too obscure: where did I forget the '&', and why would I have wanted
to write them in the first place? It could have said "did you forget to
take the address of this member function?" and it would have been clearer
to me what the message is supposed to tell me.

So, in order to be a bit less obscure, how about this wording:
  6: error: invalid use of member (did you forget the argument list?)

W.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[manu at gcc dot gnu dot org]

------- Comment #6 from manu at gcc dot gnu dot org  2009-08-05 18:19 -------
Examples where the ampersand probably makes more sense are:

g++.dg/rtti/typeid8.C
g++.dg/conversion/memfn2.C
g++.old-deja/g++.other/asm2.C

Not so sure about:

g++.dg/template/pseudodtor3.C
g++.dg/template/using14.C

So this is not as trivial.


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[bangerth at gmail dot com]

------- Comment #7 from bangerth at gmail dot com  2009-08-05 18:47 -------
(In reply to comment #6)
> Examples where the ampersand probably makes more sense are:
> 
> g++.dg/rtti/typeid8.C
> g++.dg/conversion/memfn2.C
> g++.old-deja/g++.other/asm2.C

Possibly, but in all those cases, it may also have been a
call expression:
- in typeid8.C, did the user mean
    typeid (&A::foo).name ();
  or
    typeid (A::foo()).name ();
  (assuming A::foo is static)? Certainly in the case
    typeid (foo).name ();
  it is more likely that she wanted to say foo() than &A::foo.

- in memfn2.C, 
    void (*p)() = i ? foo : foo
  was more likely meant to say
    void (*p)() = i ? foo() : foo()
  than
    void (*p)() = i ? &A::foo : &A::foo

All I really mean is that it's at the very least equally likely
that people forget the parentheses than the ampersand. Just as
another argument, people *call* functions much more often than
they *take the address* of them -- so, all things being equal,
it's probably more likely that in any given context the intent
was a call, rather than taking the address.

W.

> 
> Not so sure about:
> 
> g++.dg/template/pseudodtor3.C
> g++.dg/template/using14.C
> 
> So this is not as trivial.
> 


-- 


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[jwakely dot gcc at gmail dot com]

------- Comment #8 from jwakely dot gcc at gmail dot com  2009-08-06 09:51 -------
I don't think any of those tests would be made correct simply by replacing 'f'
with '&f'

Maybe they would have been accepted by GCC 2.95 with the ampersand present, but
current GCC correctly requires '&C::f'

I know some users want the compiler to suggest how to fix their errors, but
it's hard to make a useful suggestion for most of the nearly infinite number of
invalid expressions users can come up with.  The suggestion is misleading in
too many cases (specifically, the "did you forget the '&'?" hint doesn't solve
the problem in any of the examples given in this PR.)


-- 

jwakely dot gcc at gmail dot com changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |jwakely dot gcc at gmail dot
                   |                            |com


http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
                 CC|                            |ian at airs dot com

--- Comment #9 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-10-19 21:49:18 UTC ---
*** Bug 48630 has been marked as a duplicate of this bug. ***

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

Paolo Carlini <paolo.carlini at oracle dot com> changed:

           What    |Removed                     |Added
----------------------------------------------------------------------------
             Status|NEW                         |RESOLVED
                 CC|gcc-bugs at gcc dot gnu.org |
         Resolution|                            |FIXED
   Target Milestone|---                         |4.7.0

--- Comment #11 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-10-21 18:20:07 UTC ---
Fixed for 4.7.0.

[Bug c++/31423] Improve upon "invalid use of member (did you forget the '&' ?)"

[paolo at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=31423

--- Comment #10 from paolo at gcc dot gnu.org <paolo at gcc dot gnu.org> 2011-10-21 18:19:00 UTC ---
Author: paolo
Date: Fri Oct 21 18:18:55 2011
New Revision: 180309

URL: http://gcc.gnu.org/viewcvs?root=gcc&view=rev&rev=180309
Log:
/cp
2011-10-21  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/31423
    * typeck2.c (cxx_incomplete_type_diagnostic): Improve error message
    for invalid use of member function.

/testsuite
2011-10-21  Paolo Carlini  <paolo.carlini@oracle.com>

    PR c++/31423
    * g++.dg/parse/error43.C: New.
    * g++.dg/parse/error44.C: Likewise.

Added:
    trunk/gcc/testsuite/g++.dg/parse/error43.C
    trunk/gcc/testsuite/g++.dg/parse/error44.C
Modified:
    trunk/gcc/cp/ChangeLog
    trunk/gcc/cp/typeck2.c
    trunk/gcc/testsuite/ChangeLog