| Re: pointer to object confusion (C++ programmer, IDL n00b) [message #70722] |
Tue, 04 May 2010 08:01  |
Aram Panasenco
Messages: 41
Registered: April 2010
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Member |
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Matt Francis wrote:
> Hi All, I'm new to IDL but am a reasonable C++ coder. I'm trying to
> set up some object classes in IDL and am having some trouble.
>
> I can create custom objects and use them okay, but I can't seem to get
> a custom object to use another custom object within it. So say I have
> defined allready a class FOO, and now I want another class FOO2 which
> stores within it an instance of FOO:
>
> PRO FOO2__DEFINE
> struct = {FOO2, ...., FOO:<???>, ...}
> END
>
> What I want to know is what goes in<???>. I can't use OBJ_NEW because
> I don't know yet what arguments will be fed to FOO when it gets
> instantiated in some method of FOO2. I tried using simply OBJ_NEW() to
> get a null pointer, but then when I try something like
>
> PRO FOO2::some_method
> ...
> FOO = OBJ_NEW('FOO',[ARGS])
> END
>
> I get an error. I've tried various combinations of *FOO etc to try and
> get the above to work without success.
>
> Can anyone help me? I'm probably thinking too much like a C++
> programmer here, but I can't see that I'm trying to do something crazy
> so there must be a way to do this. Any hints?
Hi Matt!
What's going on here is: In IDL it takes two routines to initialize an
object. One is CLASSNAME__DEFINE, and the other is CLASSNAME::INIT. The
CLASSNAME__DEFINE procedure simply creates the object's class structure.
All properties of the object are initially either zeroes, or null
strings, or empty objects, or etc. CLASSNAME::INIT initializes the
properties. All arguments passed in [ARGS] in FOO = OBJ_NEW('CLASSNAME',
[ARGS]) are arguments to the INIT function. The INIT function
initializes the object's properties and returns 1 if everything went
A-ok (and 0 if the object couldn't be initialized). For example, the
CLASSNAME file could look something like this:
function CLASSNAME::INIT, arg1, arg2, arg3=arg3
if ( (n_elements(arg1) eq 0) or (n_elements(arg2) eq 0) ) then $
return, 0
self.arg1 = arg1
self.arg2 = arg2
if (n_elements(arg3) gt 0) then begin
self.arg3 = arg3
endif else begin
self.arg3 = Obj_New('SomeClass')
endelse
return, 1
end
pro CLASSNAME__DEFINE
struct = {CLASSNAME, $
arg1:0, $
arg2:'', $
arg3:Obj_New() $
}
end
And then you could create a new CLASSNAME object:
myObject = Obj_New('CLASSNAME', 2, 'Custom String')
or
myObj2 = Obj_New('SomeClass', arg1,arg2,arg3)
myObject = Obj_New('CLASSNAME', 2, 'Custom String', arg3 = myObj2)
Hope that helped you understand object creation better
~Aram Panasenco
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