Hi Sean,
let me try again without the spelling errors...
On Thu, Aug 13, 2015 at 8:58 AM, Sean P. DeNigris <s...@clipperadams.com>
wrote:
> This is a nasty one. If you pull up an inst var via Nautilus menus, any
> data
> in that variable is nil-ed out in all instances. Ouch, not fun :/ Anyone
> else experience this? Same on 5.0?
>
This is a bug in as many refactoring implementations as I'm aware of.
Essentially pull up ivar and push down ivar are decomposed into separate
class modifications, and with this approach, without some effort taken at a
higher level, ivar state is going to get lost. I saw this in VisualWorks
10 years ago. I guess it bites so infrequently and is tricky enough that
it's never been fixed. But looking at the problem it may not be that hard.
My observation is that with pull up and pull down, affected instances don't
need to be becomed, simply some of their instance variables may need to be
permuted. For example if we have C (ivx) with subclasses SCA (ivy) SCB
(ivz) and we pull up ivy to get C (ivx ivy) and SCA () and SCB (ivz) then
instances of SCA don't need to be changed at all, and instances of SCB
change from (ivx,ivz) to (ivx,ivy,ivz) with all ivy bound to nil. But if
we have C (ivi) with subclasses SCA (ivj ivk) SCB (ivl ivm) and we pull up
ivk then instances of SCA change from (ivi,ivj,ivk) to (ivi,ivk,ivj); in
become needed but the values of the second and third ivars need to be
exchanged in general instances (*) of SCA.
I think I'm right in thinking that in all cases the refactoring can be done
by modifying classes *without* doing a become on general instances of the
class from which the iv is pulled up; instead all that may be needed is a
permute.
The situation is analogous on push down, but even simpler. No instances
change size; all that may happen is that ivars may need to be permuted if
there is more than one ivar in the class from which the ivar is pushed
down, and that ivar is not the last in the class definition.
(*) a general instance of C is an instance of C or any of C's subclasses.
HTH
Cheers,
> Sean
>
_,,,^..^,,,_
best, Eliot
