On Friday, 25 July 2014 at 12:08:55 UTC, Jacob Carlborg wrote:
On 25/07/14 12:09, Jonathan M Davis wrote:
The _only_ code that would break would be code that's
_already_ broken -
code that defines opCmp in a way that's inconsistent with the
default
opEquals and then doesn't define opEquals. I see no reason to
worry
about making sure that we don't break code that's already
broken.
I see no reason why I should define opEquals when opCmp was
used for AA keys. You keep ignoring that argument.
opEquals will now be used for AA keys, not opCmp. That's why git
master generates errors when you have a struct which defines
opCmp and not opEquals, and you try and use it as an AA key. It
was done on the theory that your opEquals and opCmp might not
match (which would be buggy code to begin with, so it would be
forcing everyone to change their code just because someone might
have gotten their opEquals and opCmp wrong).
If we keep the same behavior as 2.065 but still change the AAs to
use opEquals, then there's no need to define opEquals unless the
type was buggy and defined opCmp in a way that was inconsistent
with the default opEquals and then didn't define one which was
consistent. The code will continue to work.
H.S. Teoh wants to change the default-generated opEquals to be
equivalent to lhs.opCmp(rhs) == 0 in the case where opCmp is
defined in order to avoid further breaking the code of folks
whose code is broken and didn't define opEquals when opCmp didn't
match the default.
So, if we remove the new check for a user-defined opEquals when
opCmp is defined, then you don't have to define opEquals. If we
do what H.S. Teoh suggests, then you'll have to define it if you
want to avoid the additional checks that opCmp would be doing
that opEquals wouldn't do, but if you didn't care, then you
wouldn't. If we leave it as it is in git master, then you'd
always have to define it if you defined opCmp and wanted to use
it as an AA key, and since opCmp was used for AA keys before,
that means that _every_ type which didn't define opEquals but was
used as an AA key will suddenly have to define opEquals and
toHash and will thus now be broken. So, the current situation in
git master is the worst all around.
- Jonathan M Davis
