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Re: Does this make sense? (scalar objects) [message #37242 is a reply to message #37183]

Sat, 06 December 2003 00:33

marc schellens[1]
Messages: 183
Registered: January 2000

Senior Member

JD Smith wrote:
> For objects, it's quite clear why you can't apply methods across a
> vector of object variables:
>
> IDL> objs=[obj_new('IDL_Container'), obj_new('MyFooObj')]
> IDL> objs->DoSomeMethod ; WRONG
>
> Since objects are generic pointers, and a vectors of objects can
> contain any combination of object classes, it's clear why you can't
> use this notation. The same is true of pointer arrays, for nearly the
> same reasons:
>
> IDL> ptrs=[ptr_new('string'),ptr_new(indgen(5))]
> IDL> print,*ptrs+5 ;WRONG

With the pointers it would be messy indeed (if your data is that uniform
that such an expression would really make sense, use an array).
Another thing is of course that there is no reason to not allow your
example for a single element pointer array.

With the objects though there would be no problem: Just let IDL call the
appropriate method for each individual object.
I even would think that this is more along the IDL array oriented
way.

> Single element vectors are different than scalars in several ways:
> they can be transposed, reformed, and rebinned, whereas scalars
> cannot, and they can have matrix multiplications applied to them, etc.
> A better way of asking the question is "What can't you do with scalars
> that you can do with vectors?". The answer to this consists of the
> long list of IDL vector operations discussed here daily. There may not
> be any *useful* distinctions between scalars and single-element vectors,
> but there are certainly plenty of programmatic distinctions, which would
> break backward compatibility if ignored --- hence, we are stuck with
> both.

As I said, I agree that the cannot be abolished, but
if from now on scalars could be transposed, rebined, etc.
(and reffering to my OP: method called on single object arrays),
This would not break any existing code, would it?

marc

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[Message index]

		Does this make sense? (scalar objects) By: marc schellens[1] on Wed, 03 December 2003 06:33
		Re: Does this make sense? (scalar objects) By: JD Smith on Mon, 08 December 2003 10:34
		Re: Does this make sense? (scalar objects) By: marc schellens[1] on Mon, 08 December 2003 07:10
		Re: Does this make sense? (scalar objects) By: marc schellens[1] on Sat, 06 December 2003 00:33
		Re: Does this make sense? (scalar objects) By: JD Smith on Fri, 05 December 2003 09:55
		Re: Does this make sense? (scalar objects) By: marc schellens[1] on Fri, 05 December 2003 01:58
		Re: Does this make sense? (scalar objects) By: marc schellens[1] on Fri, 05 December 2003 01:52
		Re: Does this make sense? (scalar objects) By: JD Smith on Wed, 03 December 2003 14:25
		Re: Does this make sense? (scalar objects) By: marc schellens[1] on Tue, 09 December 2003 07:59
		Re: Does this make sense? (scalar objects) By: JD Smith on Tue, 09 December 2003 11:16

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