Re: Global variables and IDL

[Struan Gray <struan.gray(at)sljus.lu.se>]

David Fanning, davidf@dfanning.com writes:

> Martin Schultz (mgs@io.harvard.edu) writes:
>>
>>    I feel ashamed. 
>
> Uh, look, this confession business has me VERY
> nervous.

<smug_git>

    I've *never* used a common block, and I strip 'em out of 
any code I get from elsewhere.

</smug_git>

    
    An alternative to common blocks that I use extensively is to
create a system variable with a unique name (it helps that I work in a
research group called 'synkrotronljusfysik') and then use it to store
the start handle of a linked list.  All my global variables are stored
by name in the list. I have utility routines to add, delete, move and
modify items, and I can create hierarchies by making any list item the
start handle to a sub-list.

    All my widget programs know that they can find things like user
preferences, large datasets and default directory names by looking for
the relevant named parameter in the list. When a widget dies, it's
cleanup routine deletes any variables associated only with itself. One
of the reasons I still use handles a lot (despite RSI's rather
sneering insistence that we use pointers these days) is that if a list
is created properly the whole thing can be disposed of automatically
simply by freeing the first handle.

    To acheive true IDLguru status I should probably objectify the
whole thing with a singleton instead of a start handle, but it works
well enough that I'm frying other fish for now.     
    
    
Struan