[REBOL] Re: Embedded Object and Scope - again...
From: joel:neely:fedex at: 10-May-2001 13:19
While discussing this with a collegue, I had a couple of added
insights.
Joel Neely wrote:
...
> As to why the same logic isn't propagated upward through
> multiple layers of enclosing objects, I can only speculate
> that RT:
>
> 1) simply didn't think of it
> 2) thought of it but didn't want to incur the expense,
> assuming that it wasn't as compelling a situation, or
> 3) implemented the context mechanism in a way that made
> it infeasible to chase up a list of "nested contexts".
>
That may sound harsher than I meant -- I wasn't criticizing,
but just trying (poorly) to say that what one can do easily
with one mechanism may or may not be easy or obvious or even
useful if one has a different conceptual mechanism.
I should also have added another option:
4) the entire concept of "embedded object" isn't really
meaningful to REBOL.
Consider this transcript:
>> obja: make object! [
[ a: 1
[ b: "hi"
[ f: func [] [print a]
[ ]
>> objb: make object! [
[ c: 10
[ d: "there"
[ x: obja
[ g: func [][print [x/b d c + x/a]]
[ ]
>> objb/g
hi there 11
>> objc: make objb [c: 20 d: "you guys"]
>> objc/g
hi you guys 21
>> obja/a: 100
== 100
>> objb/g
hi there 110
>> objc/g
hi you guys 120
>> source objc
objc:
make object! [
c: 20
d: "you guys"
x:
make object! [
a: 100
b: "hi"
f: func [][print a]
]
g: func [][print [x/b d c + x/a]]
]
Now, let't think about these questions:
1) In what sense do OBJB and OBJC "contain" OBJA?
2) In this case, don't we want OBJB and OBJC to "share"
a single OBJA (even though we don't retain its
global name)?
3) How is this different from either of the cases below?
CASE 1: "EMBEDDED" OBJECT
>> obje: make object! [
[ c: 20
[ d: "yawl"
[ x: make object! [
[ a: 2
[ b: "greetings"
[ f: func [] [print a]
[ ]
[ g: func [][print [x/b d c + x/a]]
[ ]
>> obje/g
greetings yawl 22
>> objf: make obje [c: 30]
>> objf/g
greetings yawl 32
CASE2: "PRIVATE" OBJECT
>> use [secretobj] [
[ secretobj: make object! [
[ a: 3
[ b: "howdy"
[ f: func [] [print a]
[ ]
[ objg: make object! [
[ c: 30
[ d: "youse guys"
[ x: secretobj
[ g: func [][print [x/b d c + x/a]]
[ ]
[ ]
>> objg/g
howdy youse guys 33
>> objh: make objg [a: 40 d: "aloha"]
>> objh/g
howdy aloha 33
The fact that an object is created concurrently with an
enclosing
object is time-wise coincidental, except when
the "inner" object contains words that refer to members
of the "outer" object without explicit qualification.
> >
> > 2. How can I get my descendant-embedded-object to retrieve
> > the property of it's container, the descendant-object ?
> >
>
> I can think of a couple of ways to get this effect.
>
> 1) Construct a new object in a way that strips off context
> for all words.
>
Of course this fails if you *DO* want some sharing -- if you
want the new object simply to refer to a third party also
referenced within the old object.
-jn-
