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Re: structure arguments sometimes behave like value types - why? [message #53723 is a reply to message #53605]

Mon, 23 April 2007 10:31

JD Smith
Messages: 850
Registered: December 1999

Senior Member

On Fri, 20 Apr 2007 13:26:42 -0700, justspam03 wrote:

>
> erg, addendum.
> Admittedly, in the second case the structure is not a function
> argument but a return value - I still assumed that it doesn't matter
> in the case (just as it doesn't for pointers or object references).
> Does it?
> Thanks again

In the second case, you are returning a copy of the structure from
inside the object, and then modifying that copy. The copy actually
occurred at the statement "self.val". Had you instead used a pointer
to a structure, ala:

pro structtest__define
obj = { STRUCTTEST , val: ptr_new({nullableString}) }
end

function structtest::getStruct
return, self.val
end

you could then return that *pointer*, and then modify directly the
object's internal copy. Note that you're still returning a copy of
*something* with:

b=x->getStruct()

but that something in this case is a (lightweight) copy of the pointer
to the internal structure, rather than a full copy of the structure.
However, just as it's dangerous to hand out too many sets of house
keys, it's often not a good idea to pass pointers to your important
internal data out to whomever may happen by.

Note that objects are similar to pointers in that they are (always,
unlike C++) lightweight references to variables on the global IDL
memory heap (it may help if you call them "object pointers"). They
are accessed differently, but otherwise serve a similar function: you
can make many copies, all of which refer to the same object.

JD

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[Message index]

		Re: structure arguments sometimes behave like value types - why? By: justspam03 on Fri, 20 April 2007 13:36
		Re: structure arguments sometimes behave like value types - why? By: David Fanning on Fri, 20 April 2007 14:26
		Re: structure arguments sometimes behave like value types - why? By: justspam03 on Fri, 20 April 2007 13:26
		Re: structure arguments sometimes behave like value types - why? By: JD Smith on Mon, 23 April 2007 10:31

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