| Re: Leaking objects... [message #29928] |
Wed, 27 March 2002 09:15  |
btupper
Messages: 55
Registered: January 2002
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Member |
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On Wed, 27 Mar 2002 09:29:39 -0700, David Fanning <david@dfanning.com>
wrote:
>
> You may *think* you want Obj_New to block the creation
> of a new object, but I can assure you, you *don't*. :-)
> Having only one of any particular kind of object would
> be just a tad limiting, don't you think?
>
> IDL is an inherently dangerous language. You really don't
> have any choice but to make an attempt to educate the
> people who use it. If we didn't believe this, why else
> would we all be hanging out here on the newsgroup?
Hi,
Since I am from the brute-force programming school, I immediately
thought 'What a great idea!' Having fiddled with this for a few
minutes, now I can see David's point. But a lot can be learned from
trying... now I know what that CAST keyword does.
Here's a hack that has half the behavior you describe.
If you set the destroy_previous keyword, the object will kill destroy
any existing objects of the TEST class that are not the new object.
However, if you do not set the /DESTROY_PREVIOUS keyword a new object
will *not* be created, but you will lose your reference, since the
failed object initialization returns a null object.
Ben
*****make an object
IDL> a = obj_new('test', findgen(20))
% Compiled module: TEST__DEFINE.
IDL> help, /heap
Heap Variables:
# Pointer: 1
# Object : 1
<ObjHeapVar23> STRUCT = -> TEST Array[1]
<PtrHeapVar24> FLOAT = Array[20]
IDL> help, a
A OBJREF = <ObjHeapVar23(TEST)>
*****try to make a new one of the same class
IDL> b = obj_new('test', findgen(30))
% TEST::INIT: An instance of this class already exists
IDL> help, a,b
A OBJREF = <ObjHeapVar23(TEST)>
B OBJREF = <NullObject>
IDL> help, /heap
Heap Variables:
# Pointer: 1
# Object : 1
<ObjHeapVar23> STRUCT = -> TEST Array[1]
<PtrHeapVar24> FLOAT = Array[20]
*****make a new object and destroy existing objects of the same class
*****note that a has been cleaned up
IDL> b = obj_new('test', findgen(30), /destroy_previous)
IDL> help, a,b
A OBJREF = <ObjHeapVar23>
B OBJREF = <ObjHeapVar26(TEST)>
IDL> help, /heap
Heap Variables:
# Pointer: 1
# Object : 1
<ObjHeapVar26> STRUCT = -> TEST Array[1]
<PtrHeapVar27> FLOAT = Array[30]
****** now try to redefine b (an existing object of class TEST
****** note that even though a new object is not created, the
****** null object defintion is returned to variable b
****** so you are really no further ahead
IDL> b = obj_new('test', findgen(40))
% TEST::INIT: An instance of this class already exists
IDL> help, b
B OBJREF = <NullObject>
IDL> help, /heap
Heap Variables:
# Pointer: 1
# Object : 1
<ObjHeapVar26> STRUCT = -> TEST Array[1]
<PtrHeapVar27> FLOAT = Array[30]
START HERE
pro test::cleanup
ptr_free, self.data
end
function test::init, data, destroy_previous = destroy_previous
objs = Obj_Valid(cast =1, count = count)
For i = 0L, Count-1 Do Begin
If Obj_Valid(objs[i]) EQ 1 Then Begin
If OBJ_CLASS(objs[i]) EQ 'TEST' AND objs[i] NE self
Then Begin
If KeyWord_Set(Destroy_Previous) Then Begin
Obj_Destroy, objs[i]
EndIf Else Begin
message, 'An instance of this class
already exists', /info
return, 0
EndElse
EndIf
EndIf
EndFor
if n_params() ne 1 then begin
message, 'Expecting 1 parameter', /info
return, 0
endif
self.data = ptr_new(data)
return, 1
end
pro test__define
j = { test, data: ptr_new() }
end
END HERE
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