Might there be a better way to change a character ...

# codereview

[Daniel]

Might there be a better way to change a character in a string?

fun String.setCharAt(index: Int, char: Char) = StringBuilder(this)
        .apply {
            setCharAt(index, char)
        }.toString()

Googling franticly, but I can't find an inbuild method for this

[Matteo Mirk]

you could use replaceRange from Kotlin std lib:

val s = "abcde"
println(s.replaceRange(2..2, "X"))
// -> abXde

you can encapsulate it in your extension if you like

[Matteo Mirk]

anyway “setCharAt” is misleading since strings are immutable, the closest mutating methods are in fact setCharAt() and set() on StringBuilder

[Daniel]

Good idea with the replaceRange! And agree with the setCharAt.

At the end I settled with:

fun String.replace(index: Int, newChar: Char) =
        transform {
            setCharAt(index, newChar)
        }

private fun String.transform(transform: StringBuilder.() -> Unit) =
        StringBuilder(this).apply(transform).toString()

[kevin.cianfarini]

fun String.replaceAt(c: Char, index: Int): String {
    return this.toCharArray().apply {
        set(index, c)
    }.joinToString()
}

[Matteo Mirk]

Nice @Daniel, but isn’t this shorter?

fun String.replaceAt(index: Int, newChar: Char) = replaceRange(index..index, newChar.toString())

I think it conveys the point straight when readin it, while in your solution I’d have to read two functions to understand the mechanism. Less code, improved maintainability 🙂

[Daniel]

The replaceRange is also a good option! In my case the transform is used multiple times in the file so its "known" so to speak. Also I think its nice that you immedeately see that only one char is replaced (setCharAt). But thats totally opinion of course! 🙂

[Matteo Mirk]

Sure, if it works for your codebase go for it! Didn’t want to sound pedantic, I’m just a maniac of short clean code 😆