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Re: Null
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Re: Null

  • Subject: Re: Null
  • From: Christopher Nebel <email@hidden>
  • Date: Wed, 8 Jan 2003 12:50:05 -0800
On Monday, January 6, 2003, at 06:42 PM, Doug McNutt wrote:

At 17:52 -0800 1/6/03, Christopher Nebel wrote:

Actually, there is -- it's defined in the Type Names suite:
"null", typeNull, "", { }, { },

Now I assume that means that the word "null" translates to the empty string, the empty list, or the empty record depending on the context. Is it something like a typedef? Where do I learn the definition of the compiler directive "typeNull" ?

Dang. That was supposed to be private to Chris E. Sorry about the confusion. That thing that I quoted is actually a snippet of Rez source for AppleScript's built-in dictionary. It happens to also be syntactically valid AppleScript, but that's just a coincidence.

The upshot of this is that "null" is indeed a defined identifier in AppleScript, but I don't think it means anything useful -- there's no implementation behind it. "missing value" is the thing to use in scripts.

To answer some other questions:

- "missing value" was defined in AppleScript 1.3.6.
- The Type Names suite is not intended to be visible, since it contains a bunch of only quasi-real types. Smile will show it to you anyway, I believe.
- "undf" (undefined) is AppleScript's internal "undefined" value, as opposed to "missing value", which is a real value that merely represents an undefined value. (Confused yet?) I'm of the opinion these days that we should have just revealed "undefined" instead of creating "missing value", but oh well.


--Chris Nebel
AppleScript Engineering
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References: 
 >Re: Null (From: Doug McNutt <email@hidden>)

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