| Re: keyword inheritance and object inheritance [message #29896 is a reply to message #29893] |
Sat, 23 March 2002 12:45   |
David Fanning
Messages: 11724
Registered: August 2001
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Senior Member |
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Ben Tupper (btupper@bigelow.org) writes:
> I really don't understand how to retrieve object properities when it
> comes to multiple object inheritance.
I'm pretty sure you are not alone, Ben. I *thought*
I understood it, but I spent two hours getting your
example to work. Although, as it happened, I had
the problem solved in five minutes, but I was mistyping
"grandma" as "gra*m*dma". No wonder is was always
undefined. Typical, I'm afraid. :-(
Anyway, after the jolt of Starbuck's put me onto
the right track, I think I really do understand
it how. At least I tried every single one of the
perturbations at least 5 times. :-)
Here is the rule of thumb I would use. On every
GetProperty method, I would *define* a _Ref_Extra
keyword. But on every *call* to a GetProperty method
I would use an _Extra keyword to pass the extra
structure.
For example, here is how you wrote the GetProperty
methods for your "mine" example:
;-----
; Getproperty
;-----
PRO grandmother::GetProperty, grandma = grandma
grandma = self.grandma
END
;-----
; GetProperty
;-----
PRO mother::GetProperty, mom = mom, _Ref_Extra = Extra
mom = Self.mom
Self->grandmother::GetProperty, _Extra = extra
END
;-----
; GetProperty
;-----
PRO myobj::GetProperty, me=me, _Extra = Extra
me = Self.me
Self->mother::GetProperty, _Extra = extra
END
And here is how I changed them to get them to work
as you expected them to:
;-----
; Getproperty
;-----
PRO grandmother::GetProperty, grandma = grandma, _Ref_Extra=extra
grandma = self.grandma
END
;-----
; GetProperty
;-----
PRO mother::GetProperty, mom = mom, _Ref_Extra = Extra
mom = Self.mom
Self->grandmother::GetProperty, _Extra = extra
END
;-----
; GetProperty
;-----
PRO myobj::GetProperty, me=me, _Ref_Extra = Extra
me = Self.me
Self->mother::GetProperty, _Extra = extra
END
Here is the result of my changes:
IDL> mine = Obj_new('MyObj', 'Mudd', 'Mom', 'Granny')
IDL> mine->SetProperty, Grandma = 'Nana', Mom = 'Mum', Me = 'Pooh'
IDL> mine->GetProperty, Grandma = Grandma, Mom = Mom, Me = Me
IDL> help, grandma, mom, me
GRANDMA STRING = 'Nana'
MOM STRING = 'Mum'
ME STRING = 'Pooh'
Cheers,
David
--
David W. Fanning, Ph.D.
Fanning Software Consulting
Phone: 970-221-0438, E-mail: david@dfanning.com
Coyote's Guide to IDL Programming: http://www.dfanning.com/
Toll-Free IDL Book Orders: 1-888-461-0155
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