Re: C++ PATCH for c++/88136, -Wdeprecated-copy too noisy

[Jason Merrill <jason@redhat.com>]

On Sat, Dec 8, 2018 at 1:33 PM Ville Voutilainen
<ville.voutilainen@gmail.com> wrote:
> On Sat, 8 Dec 2018 at 20:05, Ville Voutilainen
> <ville.voutilainen@gmail.com> wrote:
>
> > > New compiler releases will usually include new warnings that require
> > > some code modification to accommodate.  Why is this one particularly
> > > problematic?
> >
> > I don't think it's any more problematic than any other warning that
> > introduces new errors for fools that build with -Wall and -Werror.
> > But considering that those errors are false positives, and that
> > turning them off will in some cases require writing boiler-plate
> > (defaulted assignments), I would merely prefer having another release
> > round to get fixes for my codebase out in the wild.
>
> For what it's worth, I find it unfortunate that this deprecation and its resulting warnings end up
> making the decision on whether a "rule of 5" must be followed; correct code needs to be adjusted
> to cope with a fairly stylistic matter, with false positives and all.

I don't see it as a stylistic matter.  If you need a user-provided
copy constructor to get proper copy semantics for a class, you almost
certainly need the same thing for copy assignment.  This was too noisy
for destructors, for which it's fairly common to define a virtual
destructor just to make a class polymorphic, not because there are
significant destruction semantics.  But I don't see a similar argument
for copy constructors: in your example, there was no need for
QVariant::Private to define a copy constructor, and that seems like a
situation where a warning is reasonable, even if the code is in fact
correct.

Jason