Re: Dates gone wild
Re: Dates gone wild
- Subject: Re: Dates gone wild
- From: Nigel Garvey <email@hidden>
- Date: Wed, 10 Sep 2003 12:18:09 +0100
Chris Page wrote on Tue, 9 Sep 2003 21:53:58 -0700:
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There are objects, and there are things that refer to objects.
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Those things that refer to objects are properties, variables,
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arguments, and the items of lists and records.
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Some objects are mutable -- you can change them -- like lists and
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records, and some are not, like numbers and strings.
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More than one property, variable, argument, etc. can refer to the same
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object.
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If the object is mutable, and you change it, that change will be
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visible to everything that refers to it.
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'set' makes a variable, etc., refer to an object.
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'copy' makes a copy of an object, then makes a variable, etc. refer to
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the copy.
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That's it.
Very nicely put! :-) - though I think it might deepen Doug's confusion
about the difference between pointers and references. Everywhere where
you use "refer" above, I'd use "point" to avoid confusion with
AppleScript "references".
"Pointer" is not a term used in AppleScript, but it's used in lower-level
languages to describe a numeric value that represents the address in
memory of another value. That's what variables are beneath the surface.
Where a script says "get a", the low level action is "get the address
currently stored in the slot that the compiler associates with 'a'. This
address is the first of a couple of jumps to a value which interests us."
A "reference" *is* an entity in the AppleScript language and in
application scripting. It's not a memory pointer, but a description in
the language itself. This description invariably involves more than one
word and includes a possessive element - eg. 'item 2 of theList',
'theList of <<script>>', 'every item of theFolder whose name contains
"rabbit"', 'my aardvark', etc. References are used all the time in the
text of scripts, where they usually return the values of the described
items. In many cases, they can also be stored in variables - which is
sometimes convenient.
NG
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