[REBOL] How do I dynamically extend an object! instance Re:(5)
From: jeff:rebol at: 12-Sep-2000 21:17
> So this used-to-work but for reasons of our own protection
> has been made unworkable?
Right, what happens if you remove one of the values from the
middle of the value block? Do all the other words now point
to new values? What does the word at the end point at?
Likewise, adding a new word without a corresponding value.
> perhaps I should try another track...
Are you opposed to using blocks inside objects?
> most object based
> systems try to respect that an object should resist
> external change and only undergo transformation when
> initiated from within. you cant change an object unless it
> wants to change {reminds me of an old light bulb joke} or
> provides an access method to facilitate the change.
>
> can a function be made (within the object) that
> self-extends the object? what would that function look
> like?
Yes, using blocks.
obj: make object! [
a: [b: 2]
]
obj/a/b: 4
obj/a/b
== 4
append obj/a [c 6]
obj/a/c
== 6
etc..
If you were sadistic, you might use self modifying
functions. Here's a rather counter intuitive way to add and
remove refinements from an object:
fobj: make object! [
p-words: []
path: func refs: [/add what /remove who] body: [
either add [
path: func head insert refs to-refinement what body
append p-words what
][
either remove [
system/words/remove find p-words who
system/words/remove find refs to-refinement who
path: func refs body
][
foreach item bind p-words 'add [
print [item "==" get item]
]
]
]
]
]
fobj/add 'a
fobj/add 'b
fobj/remove 'a
Of course this isn't that much different from using
blocks, though, and you still have to add logic in the
body of the function to act on the activation of different
refinements.
Blocks are a much better and simpler way to go.
-jeff
