[REBOL] Why I don't need get-word here!
From: Patrick:Philipot:laposte at: 2-Nov-2003 18:58
Hi List,
Warning, this is a long post!
As often while coding some practical actions, I am faced with fundamentals questions.
I have some workarounds available, and it is not a matter of doing things.
What matters is understanding fully what I am doing and there is no better place to ask...
The context. My final purpose is to store in a block some faces from a layout.
These faces are extracted from the layout with something like this:
foreach face favorite/pane [
if 'fav = face/user-data [append my-favorite :face]
]
The idea is to be able to get to these faces without the need of a variable.
For now and as far as I can tell it works but ...
In a previous version of my code, I was not using the get-word :face but just
[append my-favorite face]
... and it was working the same (AFAICT).
So my questions are:
- Do I need the get-word?
- Is there a difference in the result?
To investigate on this matter, I have tried the following console session:
>> a: "Hello"
== "Hello"
>> b: "world!"
== "world!"
;
; this is my fake pane
;
>> fakepane: reduce [a b]
== ["Hello" "world!"]
;
; I am going to build two copies of fakepane
;
>> copypane1: copy []
== []
>> copypane2: copy []
== []
;
; one copy without using the get-word
;
>> foreach f fakepane [append copypane1 f]
== ["Hello" "world!"]
; one copy with the get-word
>> foreach f fakepane [append copypane2 :f]
== ["Hello" "world!"]
;
; I am changing 'a the wrong way
;
>> a: "Salut"
== "Salut"
;
; There are no changes in any block
;
>> fakepane
== ["Hello" "world!"]
>> copypane1
== ["Hello" "world!"]
>> copypane2
== ["Hello" "world!"]
;
; I think I understand this:
; a now points to a new location holding the string "Salut"
; but the block still point to the old location where the string "Hello" is.
;
;
; a smarter change (I think)
;
>>
>> clear b
== ""
>> append b "Le monde!"
== "Le monde!"
;
; now all blocks are changed
;
>> fakepane
== ["Hello" "Le monde!"]
>> copypane1
== ["Hello" "Le monde!"]
>> copypane2
== ["Hello" "Le monde!"]
;
; what is the difference between copypane1 copypane2
;
; there are not the same
; that I understand as they are not sharing the same location in memory
>> same? copypane1 copypane2
== false
; but there are equal
; that I understand as the contents are identical
>> equal? copypane1 copypane2
== true
; contents are equal and the same
>> same? copypane1/1 copypane2/1
== true
>> same? copypane1/2 copypane2/2
== true
>> equal? copypane1/1 copypane2/1
== true
>> equal? copypane1/2 copypane2/2
== true
two syntaxes, the same results, what am I missing ?
Regards
Patrick
