| Re: Object Blues [message #10750 is a reply to message #10744] |
Tue, 20 January 1998 00:00  |
mirko_vukovic
Messages: 50
Registered: January 1998
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Member |
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In article <34BFBBD7.B8EC1D48@astrosun.tn.cornell.edu>,
"J.D. Smith" <jdsmith@astrosun.tn.cornell.edu> wrote:
stuff deleted ...
> The second complaint is that IDL classes are not permitted to define
> public data members. That is, you can't access "someObject.somedata"
> anywhere outside that objec'ts own methods. Perhaps RSI saw the
> exclusion of this feature as a simplifying decision, and one that
> guarantees encapsulation. Indeed, limiting object access to its method
> procedures and functions may, at first thought, seem an obvious way to
> keep object code well-contained. However, it has other unfortunate
> consequences, usually related to the need to acquire a small group of
> parameters from an object for extensive and repeated use. The only
> solution within the current context is a GetProperty method (which, as
> you may recall, is hampered by the non-reference passing of inherited
> keywords). This is the solution implemented by IDL's object graphics.
> I maintain that an object method (such as most of the GetProperty's)
> which simply returns some subset of the member data without any
> pre-processing is wasteful and inelegant, and that the true power of
> encapsulation is in the ability to select which parts of an object to
> encapsulate.
more stuff deleted ...
jd,
the way I work on this is to have a helper object defined, name 'obj'.
This object has a method GetProperty. If I want to get a property of
some object, I have it inherit 'obj'. These days as a matter of routine
I have all my non-base objects inherit 'obj'.
'OBJ' could be expanded to include a field 'public'. This would be a
string array that would specify an objects public members. GetProperty
would check on that prior to returning the property.
This does not look terribly inconvenient.
on the other hand, can you expand on your xmanager problem? I recently
wrote my first widget routine, and promptly dispensed with xmanager using
widget_event instead. But I am still wondering how foolish I may have
been.
regards,
mirko vukovic
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