Masking all but first character in Kotlin-CodePudding

I'm afraid my solution is not very efficient:

fun String.mask() = if (isEmpty()) {
    this
} else {
    this[0]   String((1 until length).map { '*' }.toCharArray())
}

How would you do it?

CodePudding user response：

One way is to use replaceRange to do the replacing, and repeat to construct the repeated asterisks:

fun String.mask() =
    if (isEmpty())
        ""
    else
        replaceRange(1, length, "*".repeat(length - 1))

CodePudding user response：

You can just init an array full of * and set the first character too:

fun String.mask() = if (isEmpty()) {
    this
} else {
    CharArray(length) { '*' }.also { it[0] = this[0] }.joinToString(separator = "")
}

actually since the init block for the array is a function, we can just do

CharArray(length) { i -> if (i == 0) this[0] else '*' }.joinToString("")

and you can use first() instead of this[0] if that's more readable