Can somebody give me good example of using `CharSe...

# announcements

[igor.wojda]

Can somebody give me good example of using CharSequence.reduce function?

[dalexander]

This is not a “good” example in the sense that there might be better ways to do it, but here is an example using fold (I consider reduce a trap since it will crash with an empty list).
val aCount = "the rain in spain falls mainly in the plain".fold(0, {sum, cur -> sum + if(cur == 'a') { 1 } else { 0 }})

[hudsonb]

Seems odd that they require the accumulator to be a Char. reduce in Swift for example allows you to provide the initial value for the accumulator which is far more flexible/useful. I can't think of a use case for reduce, as is, that couldn't be accomplished better using other methods.

[dalexander]

Yeah, I was going to add that I’m not sure if there’s a reason to have a reduce on Char since the accumulator is a Char other than for consistency between map/reduce-able types.

[r4zzz4k]

There is also .fold, which allows you to use any type for accumulator and pass it's initial value.
https://kotlinlang.org/api/latest/jvm/stdlib/kotlin.text/fold.html
(Same goes for collections and sequences, by the way)

[hudsonb]

Right, seems like reduce may just be included for consistency as Derek suggested.

[r4zzz4k]

Most probably so, yeah.

[igor.wojda]

This confirm my suspicions that reduce may be not that useful for Char-sequence/String classes.
Thanks guys for the fold tip and thanks@r4zzz4k for info that fold have different accumulator type then reduce- this is what I needed

[karelpeeters]

Tbh I haven't had a use for reduce at all yet, lots of fold though.

[karelpeeters]

reduce on charsequences doesn't make less sense than on lists though, unless I'm missing something.

[igor.wojda]

It makes more sense on lists because accumulator and current item will have the same type as list type argument, so
String/Charsequence - accumulator/current is Char
List<Int> - accumulator/current is Int
List<String> - accumulator/current is String

So having eg. List<Int> you could sum up the items or sum up only odd items. I guess in this case we could use reduce and fold, however with String/Charsequence reduce is not an option (because accumulator/current is Char) while fold accumulator is String and current is Char

[karelpeeters]

List<Char>.reduce is exactly the same as CharSequence.reduce, right?

[r4zzz4k]

Kind of, they are generated from nearly identical code.
Actual methods:
https://github.com/JetBrains/kotlin/blob/ea0030f32409fafbc7e9b96bb4c358b7fd968a57/libraries/stdlib/common/src/generated/_Strings.kt#L1136
https://github.com/JetBrains/kotlin/blob/ea0030f32409fafbc7e9b96bb4c358b7fd968a57/libraries/stdlib/common/src/generated/_Collections.kt#L1777
Template:
https://github.com/JetBrains/kotlin/blob/ea0030f32409fafbc7e9b96bb4c358b7fd968a57/libraries/tools/kotlin-stdlib-gen/src/templates/Aggregates.kt#L729
(f_reduce and f_reduceSuper are of interest)