[REBOL] Re: How do I dynamically modify an object?
From: edanaii:cox at: 14-Jan-2003 15:41
Joel Neely wrote:
>Hi, Ed,
>
>The short answer is, "You can't!"
>
>In previous discussions, the following approach has been taken:
>
> >> example: make object! [name: "Fred" age: 5000000]
> >> example/name
> == "Fred"
> >> example/name: "Barney"
> == "Barney"
> >> source example
> example:
> make object! [
> name: "Barney"
> age: 5000000
> ]
> >> example: make example [address: "123 Bedrock Path"]
> >> source example
> example:
> make object! [
> name: "Barney"
> age: 5000000
> address: "123 Bedrock Path"
> ]
>
>But the obvious flaw is that EXAMPLE has now been set to a *new*
>object constructed from the original and the expanded spec block.
>That didn't change the original object at all. REBOL doesn't have
>AFAICT any way to expand the context of an object (or function) after
>the original definition. To show that the original did not change,
>just capture a spare reference to it, as below:
>
> >> otherref: example: make object! [name: "Fred" age: 5000000]
>
>and then evaluate the same expressions as above:
>
> >> example/name
> == "Fred"
> >> example/name: "Barney"
> == "Barney"
> >> example: make example [address: "123 Bedrock Path"]
> >> source example
> example:
> make object! [
> name: "Barney"
> age: 5000000
> address: "123 Bedrock Path"
> ]
>
>then look at the spare reference:
>
> >> source otherref
> otherref:
> make object! [
> name: "Barney"
> age: 5000000
> ]
>
>Just to prove that ADDRESS is only valid for the *new* object...
>
> >> otherref/address
> ** Script Error: Invalid path value: address
> ** Where: halt-view
> ** Near: otherref/address
> >> example/address
> == "123 Bedrock Path"
>
>Some other languages (including Perl and Python) allow new attributes
>to be added to an existing object after initial creation is long past.
>While this does open the (another ;-) door to mis-use via the creation
>of values that no longer resemble their original source code, it is
>certainly an interesting concept for a dynamic language (and one can
>use reflection/introspection to manage/follow such changes).
>
That's pretty much what I thought.
Admittedly, such abilities could get out of control and corrupt your
object. I just wanted to see if REBOL could do it.
Thanks Joe.
--
Sincerely, | Nearly all men can stand adversity, but if you
Ed Dana | want to test a man's character, give him power.
Software Developer | -- Abraham Lincoln
1Ghz Athlon Amiga |
