Quiz of the day: Why does this not work?

[Sean Kelly]

Jarrett Billingsley wrote:
> On Thu, Nov 6, 2008 at 4:23 PM, Steven Schveighoffer
> <schveiguy at yahoo.com> wrote:
>>
>> Won't make a difference.  ClassInfo does not override the default opEquals,
>> which does an is compare.
> 
> Even if it did, it's not really enough to do something like a name
> compare to see if the two typeinfos are the same.  (Actually now that
> I think about it, I think classinfo does that.. or did at some point
> in the past.)

Oops, you're right.  TypeInfo does a name comparison but ClassInfo does 
an identity comparison.

 > You would have to check and make sure that every piece
> of the type - every member, every method, all the bases - were the
> same in order for the types to be "equal".  This is obviously a
> nontrivial operation and not something you want to have happen every
> time you do a cast.

I'd expect a name comparison to be sufficient so long as the name is the 
fully qualified name of the class.  At least within a single binary. 
There's obviously the rare chance that different class implementations 
could have the same name between an app and a DLL.  So my suggestion 
wouldn't have worked in every case anyway.

> Having duplicated typeinfos is always bad news.  The best solution -
> the one that DDLs and SOs provide - is the only sane, correct one: use
> the same damn typeinfo for the same types.

Agreed.  It would be nice to gain some traction here.


Sean