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Re: global singleton object ? [message #26887 is a reply to message #26874]

Wed, 03 October 2001 08:22

Pavel A. Romashkin
Messages: 531
Registered: November 2000

Senior Member

Bob,

The following URL points to a tiny file that does what you want.
http://spot.colorado.edu/~romashki/idl/sobj_new.sav
The SOBJ_NEW does not call OBJ_NEW is a singleton object already exists,
thus avoiding OBJ_NEW overhead.
I also recommend checking out
http://spot.colorado.edu/~romashki/idl/single_set.sav
which provides essentially the same services except the contents can be
of any type, not just object. SINGLE_SET does not loop through heap
variables, fetching the only one (the named one) of interest.
The actual code is too embarassing to share, JD would not let me on the
newsgroup again :-(

s = sobj_new(/help) ; How to use it
s = sobj_new() ; Make new object
d = sobj_new() ; Get a reference to it again
help, s, d ; Make sure they are the same
; Set NO_KILL to see what it does
s -> store, obj_new('IDLgrModel'), /no_kill
s -> store ; Take a look at contents...
d -> store ; They are the same
obj_destroy, s ; And kill it (by accident).
d = sobj_new() ; NO_KILL was set, so it did not die.
; But NO_KILL is NOT set in D now, so that heap-gc, if
; ever used, does not go into an infinite loop.
d -> store ; Make sure contents are the same
; except for NO_KILL setting. Set it again if you want.

Cheers,
Pavel

P.S. The only use for a Singleton (or SINGLE_SET) that I can see is
avoiding Common blocks while
still allowing sharing some information between widget programs that may or
may not be launched independently, without using linking arguments. Or, as
people asked before, keeping a Preferences structure for the duration of a
session. When I wrote Display routines, I had to use Common block to keep
track of linked displays and the topmost one because they were intended to
be used interactively, and there is no way to define how many of them are
present and in which order. A singleton would allow this without a common
block.

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[Message index]

		Re: global singleton object ? By: R.G.S. on Wed, 03 October 2001 09:59
		Re: global singleton object ? By: Pavel A. Romashkin on Wed, 03 October 2001 08:22
		Re: global singleton object ? By: R.G.S. on Wed, 03 October 2001 06:11
		Re: global singleton object ? By: Mark Hadfield on Tue, 02 October 2001 14:47
		Re: global singleton object ? By: David Fanning on Tue, 02 October 2001 08:55
		Re: global singleton object ? By: Craig Markwardt on Wed, 03 October 2001 12:27
		Re: global singleton object ? By: Pavel A. Romashkin on Wed, 03 October 2001 10:36

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