[cfe-dev] [PATCH] Friend class cannot access protected field of parent

[John McCall]

On Jun 8, 2010, at 12:23 AM, Olivier Goffart wrote:
> So you think it is better not to try to make it work, even for the non-
> template case?

Yes.  Like I said, I don't think this is an intended feature;  I think it's a drafting
error.  [class.access.base] contains many repetitions of the phrase "member
or friend";  I think someone just wrote "member or friend" here without really
thinking.  I think when they were drafting the example in [class.protected]
they were only thinking about the effect of the protected access restriction, not
whether the member itself was accessible from the naming class.  I'm willing
to consider evidence in the form of a DR that I'm wrong, but I don't really want
to implement the rule, and I'm not going to implement it as long as it's
undecidable.

Since I think this only affects people trying to compile Qt itself (rather than
people relying on Qt headers), I don't think it qualifies for a workaround.
It should be really easy to fix in the source, though.

Also, thank you for reminding me to add "introduces crazy dependencies on
instantiation order" to the list of reasons why this is a terrible mistake. :)

John.