Return from lambdas or Kotlin: 'return' is

问题:

I am trying to write function which will tell me that string is nice, nice means string has at least one repetition of letters in the string. But I can't to make return from lambda, it's always return false, though condition in if statement passed. Can somebody explain me how make return?

I have tried to write return, but IDEA gave me the message Kotlin: 'return' is not allowed here

fun main(args: Array<String>) {
    println("sddfsdf".isNice())
}

fun String.isNice(): Boolean {
    val hasRepeat = {
        for (i in 0 .. (length - 2)) {
            if (subSequence(i, i + 2).toSet().size == 1) {
                true
                println(subSequence(i, i + 2))
            }
        }
        false
    }

    return hasRepeat()
}

ouput is:

dd
false

回答1:

You can label lambda and then use labeled return:

fun String.isNice(): Boolean {
    val hasRepeat = hasRepeat@ {
        for (i in 0 .. (length - 2)) {
            if (subSequence(i, i + 2).toSet().size == 1) {
                return@hasRepeat true
                println(subSequence(i, i + 2)) // <-- note that this line is unreachable
            }
        }
        false
    }

    return hasRepeat()
}

or you can use named local function, if you do not need hasRepeat to be function reference:

fun String.isNice(): Boolean {
    fun hasRepeat(): Boolean {
        for (i in 0 .. (length - 2)) {
            if (subSequence(i, i + 2).toSet().size == 1) {
                return true
            }
        }
        return false
    }

    return hasRepeat()
}

回答2:

You cannot do a non-local return inside a lambda but you can change your lambda to an anonymous function:

fun String.isNice(): Boolean {
    val hasRepeat = fun(): Boolean {
        for (i in 0..(length - 2)) {
            if (subSequence(i, i + 2).toSet().size == 1) {
                return true
            }
        }
        return false
    }

    return hasRepeat()
}