[Bug libstdc++/49174] New: numeric_limits<T> template is a struct not a class

[Bug libstdc++/49174] New: numeric_limits<T> template is a struct not a class

[frank@kingswood-consulting.co.uk]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49174

           Summary: numeric_limits<T> template is a struct not a class
           Product: gcc
           Version: 4.6.0
            Status: UNCONFIRMED
          Severity: minor
          Priority: P3
         Component: libstdc++
        AssignedTo: unassigned@gcc.gnu.org
        ReportedBy: frank@kingswood-consulting.co.uk


ISO 14882:1998 defines in 18.2.1.4 the contents of <limits>
   template<class T> class numeric_limits

The libstdc++ header defines this as
   template<class T> struct numeric_limits

[Bug libstdc++/49174] numeric_limits<T> template is a struct not a class

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49174

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

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

--- Comment #1 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-05-26 14:47:05 UTC ---
There is absolutely no difference between a struct and a class in C++, besides
access control, and in 18.2.1.1 there is a 'public:' at the beginning.

[Bug libstdc++/49174] numeric_limits<T> template is a struct not a class

[frank@kingswood-consulting.co.uk]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49174

--- Comment #2 from frank@kingswood-consulting.co.uk 2011-05-26 18:25:03 UTC ---
I realize struct and class are interchangeable.
llvm with -Wextra finds the difference worth warning about.

[Bug libstdc++/49174] numeric_limits<T> template is a struct not a class

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49174

--- Comment #3 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-05-26 18:52:55 UTC ---
In my experience as implementer, the equivalence between struct and class often
makes for conciseness, like in this case: we know everything will be public
anyway, thus we can spare the access-specifier. In the specific case of limits
we are also consistent, we use 'struct' both for the primary and the
specializations, thus there is *really* nothing to possibly warn about.

[Bug libstdc++/49174] numeric_limits<T> template is a struct not a class

[pinskia at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49174

--- Comment #4 from Andrew Pinski <pinskia at gcc dot gnu.org> 2011-05-26 19:22:13 UTC ---
Note the reason why clang warns is because of some body at MS decided that
class and struct would act slightly different.  I think we should not follow MS
here and not warn about this.  I think clang should not warn about it either by
default but we have no control over that.

[Bug libstdc++/49174] numeric_limits<T> template is a struct not a class

[paolo.carlini at oracle dot com]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49174

--- Comment #5 from Paolo Carlini <paolo.carlini at oracle dot com> 2011-05-26 19:25:04 UTC ---
Over my dead body Andrew ;)

[Bug libstdc++/49174] numeric_limits<T> template is a struct not a class

[frank@kingswood-consulting.co.uk]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49174

--- Comment #6 from Frank Kingswood <frank@kingswood-consulting.co.uk> 2011-05-28 08:41:05 UTC ---
What's so bad about following the ISO specification to the letter?

[Bug libstdc++/49174] numeric_limits<T> template is a struct not a class

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49174

--- Comment #7 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-05-28 12:01:49 UTC ---
(In reply to comment #6)
> What's so bad about following the ISO specification to the letter?

Because it makes absolutely no difference except to those who maintain the
code, and we've expressed our preference - why do you care?

libstdc++ is the GCC standard library, not clang's, so the fact someone else's
compiler doesn't like it is not our problem

[Bug libstdc++/49174] numeric_limits<T> template is a struct not a class

[redi at gcc dot gnu.org]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=49174

--- Comment #8 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-05-28 12:13:06 UTC ---
Besides which, we *are* following it to the letter, see 1.9 [intro.execution]
paragraph 1 and the accompanying footnote

5) This provision is sometimes called the “as-if” rule, because an
implementation is free to disregard any requirement of this
International Standard as long as the result is as if the requirement had been
obeyed, as far as can be determined from the
observable behavior of the program. For instance, an actual implementation need
not evaluate part of an expression if it can
deduce that its value is not used and that no side effects affecting the
observable behavior of the program are produced.


If there's an observable difference then it's a problem, otherwise it's
irrelevant.