As someone else already pointed out, the standard way to copy
part of any array-like sequence is
aSequence copyFrom: firstIncludedIndex to: lastIncludedIndex
How could you have found this by yourself?
>From the background, either
Click-select Tools-select Playground
or hold Ctrl down while typing OW (for Open Workspace).
In the new Playground/workspace, type
String
then Ctrl-B. You now have a five-pane browser open on
String.
About half way down the third panel on the top you will see
converting
copying
displaying
Click on copying.
Guess what? You WON'T see anything that looks relevant!
Maybe it's in an ancestral class. So look at the buttons
under the top row of panes:
All packages Scoped view | Flat Hier | Inst side Class side | ...
Hier looks promising. Click it.
Now in the second pane you will see
ProtoObject
Object
Collection
SequenceableCollection
ArrayedCollection
String
...
Select the parent class, ArrayedCollection.
Nope, nothing promising there either!
Select the grandparent class, SequenceableCollection.
And now the 'copying' method category has quite a few
potentially interesting methods, including #copyFrom:to:.
There are four other related methods that I would argue
are in the wrong category:
allButFirst
allButFirst: count
allButLast
allButLast: count
are in the 'accessing' category.
If you want something a bit more flexible,
you could add
drop: d take: t
"Discard the first |d| elements of the receiver if d >= 0.
Discard the last |d| elements of the receiver if d <= 0.
Return the first |t| elements of the result if t >= 0.
Return the last |t| elements of the result if t <= 0.
The result is the same kind of collection as the receiver."
|lb ub n|
n := self size.
d abs >= n ifTrue: [^self copyEmpty].
d < 0
ifTrue: [lb := 1. ub := n + d]
ifFalse: [lb := d+1. ub := n].
ub - lb + 1 <= t abs ifFalse: [
t < 0
ifTrue: [lb := ub + t + 1]
ifFalse: [ub := lb + t - 1]].
^self copyFrom: lb to: ub
Now I would like to suggest that you not use anything like this
*directly*. Go back to the Playground, and evaluate
String with: (Character codePoint: 256) <Ctrl-P>
The answer is 'Ā'. Pharo supports Unicode. Now try
String with: $A with: (Character codePoint: 16r0304)
In Pharo, the result looks like A followed by a separate
macron, but when it's pasted into HTML it displays
correctly as 'Ā'. Pharo doesn't *quite* support Unicode.
If it did, the two strings with different lengths and no
codepoint in common would display exactly the same.
The Unicode standard finds it necessary to distinguish
between characters, glyphs, graphemes, grapheme clusters,
codepoints, and a couple of other things. A Smalltalk
String is a sequence of *codepoints*, not a sequence of
"characters". There is no upper bound on the number of
codepoints that may be needed to encode one "character"
as the end user sees it, and from there on it gets
*complicated*.
For over 20 years, it hasn't really made sense to think
of a string as a simply indexed sequence of characters.
Integer indices are a useful implementation-level detail
for remembering bounds from some "higher level" matching
technique, but are much less useful than you might expect.
On Wed, 6 Mar 2019 at 12:00, Craig Johnson <cr...@hivemind.net> wrote:
> Hi All,
>
>
>
> I was trying to figure an elegant way to slice strings (Python style), and
> came up empty.
>
>
>
> What is the simplest way to copy characters between positions 4 and 8 from
> a string in Pharo?
>
>
>
> Craig
>
