global variables

David Vaughan drvaughan55 at mac.com
Mon Aug 26 22:07:01 CDT 2002


On Tuesday, August 27, 2002, at 12:52 , Rob Cozens wrote:

>>> The global keyword is adopted from HyperCard 1.0, and has been a part 
>>> of all
>>> xTalk implementation since.  How else would the engine know whether 
>>> to treat
>>> a variable as local or global without such a keyword?
>>
>> Presumably it would maintain a list and then every time you used a 
>> variable, it would have to check to see if it was in the list.  But 
>> once you added a variable to the list, you would never have to add it 
>> again, which would be a nice feature.
>
> Whoa Mark,
>
> That would mean every time one wrote a handler one would have to check 
> EVERY local variable name to make sure it was not on the global list.  
> This would include handlers in other people's stacks as well as your 
> own.
>
> As an aside, just as Revolution has less need to use externals than 
> HyperCard, it also has less need to use global variables.  One can 
> define local variables that are shared by all handlers in a script and 
> whose values persist until the stack is closed.

...and that is the key: declaring global or local variables at the top 
of scripts rather than in handlers. It was one of the immediate changes 
I made to HyperCard-patterns of scripting. Better yet, I basically never 
use globals anyway. On the occasions a local declaration will not serve, 
I prefer a custom property (of any suitable object). It is globally 
accessible, persistent and non-conflicting with other variable naming.

regards
David
>
> I was able to replace all globals in my original HyperCard library 
> design with locally-declared variables.
> --
> Rob Cozens
> CCW, Serendipity Software Company
> http://www.oenolog.com/who.htm
>
> "And I, which was two fooles, do so grow three;
> Who are a little wise, the best fooles bee."
>
> from "The Triple Foole" by John Donne (1572-1631)
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>




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