| Re: It seems that there is *a bit* polymorphism in IDL. [message #40540 is a reply to message #40464] |
Thu, 12 August 2004 10:28   |
JD Smith
Messages: 850
Registered: December 1999
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Senior Member |
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On Wed, 11 Aug 2004 21:05:49 -0600, David Fanning wrote:
> David Fanning writes:
>
>> Amen to this! In fact, generalized GetProperty functions are so easy to
>> write and so useful for obtaining any *single* object property, that
>> *all* your objects should have one, along with the usual GetProperty
>> procedure. :-)
>>
>> http://www.dfanning.com/tips/getproperty.html
>
> OK, IDL 6.1 arrived this afternoon, so here is a programming quiz for all
> of you who are not currently Members in Good Standing with IEPA
> (http://www.dfanning.com/misc_tips/iepa.html). (This includes all of you
> who have forgotten to pay your dues this month.)
>
> Use the SCOPE_VARNAME function with the REF_EXTRA keyword to write a short
> general purpose GETPROPERTY *procedure* method that'll return any member
> variables referenced via keyword names
At long last... legitimized access to the oft-defamed (and poorly
named) ROUTINE_NAMES() variable functionality! I can now feel quite
justified in my various out-of-scope variable slinging (which is used
heavily in IDLWAVE debugging). Very cool new _REF_EXTRA keyword in
SCORE_VARFETCH should enable lots of neat functionality, including the
one you mention (I presume you meant that one instead of
SCOPE_VARNAME).
Also welcome are the left-aligned and zero-padded updates for the
FORMAT codes.
On the original topic, I was going to suggest a general purpose
execute-based GetProperty function like:
function MyClass::GetProperty,_EXTRA=e
if n_elements(e) eq 0 then return,-1
prop=(tag_names(e))[0]
void=execute('self->GetProperty,'+prop+'=ans')
return,ans
end
which uses the GetProperty procedure method (which, in my case, often
does more than simply return a field of the class structure). This uses
EXECUTE as well, so is to be avoided for VM code. Your requested
solution is also trivial:
pro MyClass::GetProperty,_REF_EXTRA=e
tags=tag_names(create_struct(NAME=obj_class(self)))
for i=0,n_elements(e)-1 do begin
wh=where(tags eq e[i],cnt)
if cnt eq 0 then continue
(scope_varfetch(e[i],/REF_EXTRA))=self.(wh[0])
endfor
end
Note this uses the new (I think, don't have IDL 6.1 yet) functionality
for 'CREATE_STRUCT,NAME=' I had just pined for: the ability to create a
named structure programmatically without resorting to EXECUTE.
This still doesn't solve the problem of enabling rapid access to object
data members: this function will take many hundreds or thousands of
times longer to execute than a similar structure field dereference would
take. I find that for speed reasons I'm often caching copies of some
object's internal fields inside of other objects, which can lead to
problems if the cache is not kept up to date. Encapsulation is great,
but the penalty for routine calls is too high for some event-driven
situations to make good use of it.
I suspect you should also be able to do something clever with
SCOPE_VARFETCH and a GetProperty function, like:
function MyClass::GetProperty,_REF_EXTRA=e
self->GetProperty,_EXTRA=e
return,scope_varfetch(e[0],/REF_EXTRA)
end
Obviously untested, since I don't have 6.1.
Fun stuff.
JD
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