| Re: Generating keyword parameters from strings [message #67395] |
Mon, 27 July 2009 14:26  |
Kenneth P. Bowman
Messages: 585
Registered: May 2000
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Senior Member |
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In article <MPG.24d76d9aa33164a7989836@news.giganews.com>,
David Fanning <news@dfanning.com> wrote:
> Paul van Delst writes:
>
>> It certainly would make it easier for new users who wonder what
>> they've done wrong until they discover you can't pass arguments *out* from
>> procedures...
>
> I don't think new users are meant to use direct
> graphics commands. That's why they are made as
> difficult to use as possible. These problems don't
> exist with iTools. :-)
>
> Cheers,
>
> David
>
> P.S. *Are* there any new users? I can't think of
> one person using iTools, with the possible exception
> of Ken Bowman, who always seems to be complaining
> about them. ;-)
Well, I don't teach iTools graphics when in my beginning IDL
course. The students are supposed to be learning to program,
not point, click, and drag. And *programming* the iTools is not
for the faint of heart.
I do use iTools when I have to do 3-D interactive graphics because
I am not smart enough to write my own object graphics programs.
Cheers, Ken
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| Re: Generating keyword parameters from strings [message #67439 is a reply to message #67432] |
Thu, 23 July 2009 05:14  |
Jeremy Bailin
Messages: 618
Registered: April 2008
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Senior Member |
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On Jul 22, 8:01 pm, Giorgio <giorgiol...@gmail.com> wrote:
> I can image something with create_struct and call_method. But I do not
> know if this will work, like call_method, 'GetProperty', object,
> _Extra = create_struct('keyword', value)
>
> Giorgio
Yeah, that's what AUGMENT_INHERITED_KEYWORD does (note that you can
give it an undefined variable to start off with, if you're not
actually augmenting an existing structure):
http://web.astroconst.org/jbiu/jbiu-doc/misc/augment_inherit ed_keyword.html
-Jeremy.
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| Re: Generating keyword parameters from strings [message #67445 is a reply to message #67443] |
Wed, 22 July 2009 15:55 |
Michael Galloy
Messages: 1114
Registered: April 2006
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Senior Member |
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Eric Hudson wrote:
> Hi,
>
> I guess I was unclear, sorry.
>
> What I mean is that I want to take a string and turn it into a
> keyword. So continuing my above example:
>
>
> function GetProperty, object, propertyName
> ; The below line is pseudocode -- what I want
> object->GetProperty, 'propertyName'=value
> ; using execute I'd say:
> ; ok = execute('object->GetProperty, '+propertyName+'=value')
> ; but I'm wondering if there is another way to do this
> ; that will work when execute is forbidden
> return, value
> end
>
> pro TestGet
> myObj = obj_new('IDLgrPalette')
> myvalue = GetProperty(myObj,'N_COLORS')
> ; Should be functionally equivalent to
> ; myObj->GetProperty, N_colors=myValue
> end
>
> That is, my 'GetProperty' function has to take the string 'N_COLORS'
> and then call the GetProperty method using that STRING as a reference
> keyword. It is this functionality that I'm interested in (I'm just
> using GetProperty as an example).
I don't think this is possible without a) using EXECUTE or b) writing a
temporary IDL .pro file. I messed around with the REF_EXTRA keyword to
SCOPE_VARFETCH, but I couldn't get what you wanted.
Mike
--
www.michaelgalloy.com
Associate Research Scientist
Tech-X Corporation
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| Re: Generating keyword parameters from strings [message #67446 is a reply to message #67445] |
Wed, 22 July 2009 13:46 |
Eric Hudson
Messages: 19
Registered: June 2006
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Junior Member |
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Hi,
I guess I was unclear, sorry.
What I mean is that I want to take a string and turn it into a
keyword. So continuing my above example:
function GetProperty, object, propertyName
; The below line is pseudocode -- what I want
object->GetProperty, 'propertyName'=value
; using execute I'd say:
; ok = execute('object->GetProperty, '+propertyName+'=value')
; but I'm wondering if there is another way to do this
; that will work when execute is forbidden
return, value
end
pro TestGet
myObj = obj_new('IDLgrPalette')
myvalue = GetProperty(myObj,'N_COLORS')
; Should be functionally equivalent to
; myObj->GetProperty, N_colors=myValue
end
That is, my 'GetProperty' function has to take the string 'N_COLORS'
and then call the GetProperty method using that STRING as a reference
keyword. It is this functionality that I'm interested in (I'm just
using GetProperty as an example).
Thanks,
Eric
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| Re: Generating keyword parameters from strings [message #67455 is a reply to message #67454] |
Wed, 22 July 2009 11:00 |
Paul Van Delst[1]
Messages: 1157
Registered: April 2002
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Senior Member |
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Eric Hudson wrote:
> Hi,
>
> Does anyone know of a method of taking a string and turning it into a
> keyword parameter? As an example, say I want to write a function:
>
> function GetProperty, object, propertyName
> object->GetProperty, 'propertyName'=value ; This is pseudocode --
> this line is what I need
> return, value
> end
>
> Obviously I can write this using execute, but I'd prefer to avoid that
> if at all possible.
> Also, although I use the GetProperty method as an example, this is a
> more generic question about generating keyword parameter calls (so,
> for example, David's nice discussion of a general GetProperty method
> http://www.dfanning.com/tips/getproperty.html doesn't help here).
>
> If I were just setting a value this would be easy to do with _EXTRA by
> making my own structure. But for getting values it doesn't seem like
> there is an easy equivalent (it would be nice to just make a
> _REF_EXTRA structure if it behaved equivalent to _EXTRA but it seems
> it doesn't).
?
I use _EXTRA for my Set_Property() methods, and _REF_EXTRA for my Get_Property() methods
when I have superclasses and it seems to work fine. For example:
PRO SUBCLASS::Set_Property, $
....subclass property keywords here...
_EXTRA = Extra ; Keywords passed onto SUPERCLASS::Set_Property
...set the subclass properties....
; Set the superclass properties
self->SUPERCLASS::Set_Property, _EXTRA = Extra
END
PRO SUBCLASS::Get_Property, $
....subclass property keywords here...
_REF_EXTRA = Extra ; Keywords passed onto SUPERCLASS::Get_Property
...get the subclass properties....
; Get the superclass properties
self->SUPERCLASS::Get_Property, _EXTRA = Extra
END
I really don't understand why, in the SUBCLASS::Get_Property method, I can get away with
using the _EXTRA keyword to the SUPERCLASS::Get_Property method, but it works. Go figure.
cheers,
paulv
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| Re: Generating keyword parameters from strings [message #67506 is a reply to message #67432] |
Thu, 30 July 2009 08:21 |
JDS
Messages: 94
Registered: March 2009
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Member |
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On Jul 23, 3:48 pm, Paul van Delst <paul.vande...@noaa.gov> wrote:
> David Fanning wrote:
>> Paul van Delst writes:
>
>>> I really don't understand why, in the SUBCLASS::Get_Property method, I can get away with
>>> using the _EXTRA keyword to the SUPERCLASS::Get_Property method, but it works. Go figure.
>
>> The rule is you use _REF_EXTRA (or _REF_STRICT_EXTRA, etc) on
>> the procedure or function *definition* line, but *all* extra
>> parameters are to be *passed* with _EXTRA.
>
> Ah, o.k. A nice, simple rule to remember.
>
> Of course it would be nicer if I didn't have to remember it at all. Passing
> arguments/keywords by reference or value is an implementation detail the user shouldn't be
> concerned with. Having to consider it in IDL OO programming is mildly ironic.
Nicety is in the eye of the beholder. At the time I proposed
_REF_EXTRA and it was added to IDL 5.1, the IDL programmer who
implemented it was very proud that it required only a single change to
the routine definition line, not all the _EXTRA calls themselves. At
the time, I objected to the duplicate interface. But I came to
understand that it was an absolute requirement due to a simple but
frustrating issue: various people (including those posting to this
thread!) routinely build or augment their own _EXTRA structures.
If you think about it, there is no way (without inventing a new type
of IDL variable) to simultaneously change the semantics of _EXTRA to
allow passing by reference, and *not* break all of those sneaky codes
which are poking around in _EXTRA structure themselves. So we have
only ourselves to blame.
JD
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