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Title
e

Ellen Spertus

02/02/2020, 8:25 PM
// 1
var c = 0 // count of number of times this substitution is made in text
val newText = text.replace(re) {
    c += 1
    sub
}
or
// 2
val c = re.findAll(text).asSequence().count()
val newText = text.replace(re, sub)
or something better?
c

Czar

02/02/2020, 9:11 PM
if performance is a concern:
val text = "abcdbdecbcd"
val matcher = "b".toPattern().matcher(text)
val sub = "Z"
var counter = 0
val newText = if(matcher.find()) {
	buildString(text.length) {
		do {
			counter++
			matcher.appendReplacement(this, sub)
		} while (matcher.find())
		matcher.appendTail(this)
	}
} else {
	text
}
// test:
check(counter == 3)
check(newText == "aZcdZdecZcd")
🤔 1
e

Ellen Spertus

02/02/2020, 9:12 PM
FYI, replacement string is guaranteed to be no longer than the original string
👌 1
I’m trying out the code in the KotlinPlayground. It made me replace
StringBuilder
with
StringBuffer
.
c

Czar

02/02/2020, 9:15 PM
huh, that should not be necessary, in fact
StringBuilder
is better choice in this case.
e

Ellen Spertus

02/02/2020, 9:16 PM
Agreed. No concurrency.
c

Czar

02/02/2020, 9:16 PM
By the way, if you use IntelliJ, Scratch files are awesome as a replacement for KotlinPlayground
e

Ellen Spertus

02/02/2020, 9:16 PM
I see that your code works but I don’t understand how the unchanged characters end up in the output string.
c

Czar

02/02/2020, 9:17 PM
That's how matcher.appendReplacement is coded, take a look at its source if interested.
e

Ellen Spertus

02/02/2020, 9:17 PM
Got it. I’ll RTFM.
I’ve never seen a function like that when working with regexps. Thanks for pointing me to it.
c

Czar

02/02/2020, 9:19 PM
in fact maybe I was wrong to think it'll have best performance, seems it creates an additional StringBuilder on each replacement.
1
e

Ellen Spertus

02/02/2020, 9:19 PM
I’d say that clarity and simplicity are more important to me than performance.
c

Czar

02/02/2020, 9:20 PM
do you need
re
to be a regex, or is it just a normal substring replacement?
e

Ellen Spertus

02/02/2020, 9:21 PM
The
c += 1
in my original code (transliterated from JS) rubbed me the wrong way because functional programming, but there’s no need to pretend I’m in a purely functional language.
It’s a regex made by combining a bunch of individual strings into a regex (e.g.,
\\b(foo|bar|baz)\\b
).
c

Czar

02/02/2020, 9:23 PM
you're performing an operation where you have two outputs - changed string and number of replacements, it is possible to do it without
counter++
, but won't be as readable
1
e

Ellen Spertus

02/02/2020, 9:23 PM
I don’t feel the need to be more efficient than the original JS code, but I do want it to look like it was written by a Kotlin programmer, not a JS programmer…
or a Scheme programmer.
😀 2
c

Czar

02/02/2020, 9:24 PM
there are people who write very functional code in Kotlin, just look at the Arrow library
e

Ellen Spertus

02/02/2020, 9:24 PM
Yes, or I’d be duplicating the work, as shown in
2
.
I think I just need to get the middle ground between needlessly imperative and needlessly pure, while writing idiomatic Kotlin code. I greatly appreciate all of your help. I’m the only Kotlin programmer on my team, and just learned it in the fall, so this Slack has been very helpful.
I’ve been programming in Java since the 90s so have a lot to unlearn.
c

Czar

02/02/2020, 9:34 PM
I've made a mistake, fixed now.
e

Ellen Spertus

02/02/2020, 9:35 PM
Where was the mistake?
c

Czar

02/02/2020, 9:35 PM
there was no appendTail after the while loop
✔️ 1
I've thought about your requirements some more and it seems to me this would be a better version for you:
val text = "abcdbdecbdz"
val matcher = "(b)".toPattern().matcher(text)
val sub = "Z"
val count = matcher.results().count()
val newText = matcher.replaceAll(sub)
it's much more readable and understandable than the loop and counter var version. The only drawback is that search is performed twice, as `replaceAll`resets the matcher state.
e

Ellen Spertus

02/02/2020, 9:44 PM
Very nice!
I have a Map where I need to look up each substitution, but your solution will generalize to that.
c

Czar

02/02/2020, 9:50 PM
what do you mean? how does that map look?
e

Ellen Spertus

02/02/2020, 9:53 PM
Actually, never mind. I was thinking of a different part of my code.
I tried your code today but got
Unresolved reference: results
on the second-to-last line.
c

Czar

02/05/2020, 6:47 PM
Oh, you're probably on Java 1.8 then, the
results()
was added in JDK9 I believe
1
e

Ellen Spertus

02/05/2020, 6:53 PM
Yeah, I’m using 1.8.
I’m on Android, which doesn’t support 1.9. :android:
Thanks again for all of your help!
c

Czar

02/05/2020, 6:54 PM
NP, glad I could help