Re: Variable Ponderance
Re: Variable Ponderance
- Subject: Re: Variable Ponderance
- From: Paul Berkowitz <email@hidden>
- Date: Thu, 30 Sep 2004 10:37:31 -0700
You need to read up on lists and on scope in the AppleScript Language Guide
or, better, in Matt Neuburg's AppleScript: The Definitive Guide. (Matt's
very good on this.)
Lists, records, dates and script objects are "data sharing" - i.e. mutable
in place. Furthermore, top-level variables are global in scope unless
specifically declared local. So unless you declare y to be local in your
handler, or at the top level of the script, or both, it's going to be
global.
--
Paul Berkowitz
> From: Ben Waldie <email@hidden>
> Date: Thu, 30 Sep 2004 13:27:09 -0400
> To: AppleScript User's List <email@hidden>
> Subject: Variable Ponderance
>
> I think I have noticed this before, but just never questioned it.
>
> In the following examples, I set a local variable to a value, and then
> pass that variable down to a handler as a parameter. In the handler, I
> change the value of this parameter. I would expect this change to be
> local to the handler only, and not global to the script. So, at the
> main level of the script, I would expect the variable to retain it's
> original value, no matter what happens to it in the handler.
>
> In the first example, I pass down a variable containing a number,
> completely change it to a value of 2, and the variable at the top level
> of my script behaves as I would expect, retaining its original value.
> In the second and third examples though, I pass down a variable
> containing a list or a record, modify part of the list or record, and
> the variable at the top level of my script does not behave as I would
> expect. In these 2 cases, the main script treats the variable as it if
> is a global, remembering the change I made in the handler. This
> appears to occur only when manipulating the variable, and not when
> changing it completely. Is this the intended behavior?
> --------------------
> EXAMPLE 1
> --------------------
> set x to 1
> doSomething(x)
> return x
> --> 1 -- I would expect 1
>
> on doSomething(y)
> set y to 2
> end doSomethingElse
> --------------------
> EXAMPLE 2
> --------------------
> set x to {1, 2, 3}
> doSomething(x)
> return x
> --> {2,2,3} -- I would expect {1,2,3}
>
> on doSomething(y)
> set item 1 of y to 2
> end doSomething
> --------------------
> EXAMPLE 3
> --------------------
> set x to {name:"Ben"}
> doSomething(x)
> return x
> --> {name:"Waldie"} -- I would expect {name:"Ben"}
>
> on doSomething(y)
> set name of y to "Waldie"
> end doSomething
> --------------------
>
>
> -Ben
>
> Benjamin S. Waldie
> President & CEO
> Automated Workflows, LLC
> 610.935.0652
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