| Re: Storing !NULL in struct [message #83597 is a reply to message #83531] |
Mon, 18 March 2013 11:26   |
Yngvar Larsen
Messages: 134
Registered: January 2010
|
Senior Member |
|
|
On Monday, 18 March 2013 17:48:54 UTC+1, Mike Galloy wrote:
> On 3/18/13 6:40 AM, Tom Grydeland wrote:
>
>
> I think what you are showing here is that any variable passed by value
> does not end up modified at the calling level.
Right.
> It doesn't work for arrays of structures either:
>
> IDL> sarr = replicate({ foo: 0 }, 10)
> IDL> modify, sarr[0]
> IDL> print, sarr[0]
> { 0}
Yes, but you can still modify an element, or even a range of elements, of a structure array at your current calling level:
IDL> sarr[0].foo = 4
IDL> print, sarr[0].foo
4
IDL> sarr[3:5].foo = 4
IDL> print, sarr[0:6].foo
4 0 0 4 4 4 0
This is not the case for lists, as already discussed:
IDL> larr = list(length=10) & for n=0, 9 do larr[n] = {foo: 0}
IDL> print, larr[0].foo
0
IDL> larr[0].foo = 4
% Attempt to store into an expression: Structure reference.
% Execution halted at: $MAIN$
I fail to see why the latter isn't allowed. This means that if you still want to modify structures within your list, you need to do something like this
IDL> tmp = larr[0]
IDL> tmp.foo = 4
IDL> larr[0] = tmp
IDL> print, larr[0].foo
4
This seems silly to me. What is the purpose of not allowing this?
Switching to hash tables instead of structures as general purpose data structure is of course a very good strategy in 2013, but I have at least 10 years worth of legacy code which already heavily (mis-)uses the anonymous structure as a "hash table light" with case insensitive keys.
--
Yngvar
|
|
|
|
comp.lang.idl-pvwave archive
Members
Search
Help
Login
Home
