[Bug c++/44499] No default constructor available

["redi at gcc dot gnu.org" <gcc-bugzilla at gcc dot gnu dot org>]

http://gcc.gnu.org/bugzilla/show_bug.cgi?id=44499

--- Comment #14 from Jonathan Wakely <redi at gcc dot gnu.org> 2011-03-04 11:23:41 UTC ---
(In reply to comment #13)
> (In reply to comment #12)
> > Manu, can we close this?
> 
> @Jonathan
> 
> I still think that the messages of Comeau and Clang are better than GCC's. I
> will try for 4.7 to produce a patch to change the message to be like:
> 
> error: default initialization of const object 'g_d' requires a user-provided
> default constructor [-fpermissive]
> note: 'const class D' has no user-provided default constructor
> 
> Do you agree? 

Sure, if you still plan to improve it let's definitely keep it open.

> (I'd like to keep the note to jump to the declaration of class D).

Ah yes, that's useful.

In the spirit of providing "fix it" hints, I think the EDG diagnostic is
better.  There are two ways to avoid the error:

1) Add a default constructor.  This changes the type in non-trivial ways with
potentially large side-effects in terms of POD-ness, affecting all users of the
code and requiring recompilation. It's not even possible for classes defined in
third-party headers.

2) Use an initializer.  This doesn't change the type and is a purely local
change.

The second option is probably the right one in most cases  :)
"Expert" users who know what they're doing can choose to alter the class, but I
don't think we should suggest they do so.

How about this:

error: Const object 'g_d' requires an initializer [-fpermissive]
note: 'const class D' has no user-provided default constructor

The error refers to the variable's location and says an initializer is needed.
The note refers to the class' location  and says it has no default constructor.