Lambdas and Higher-Order Functions

Capturing Variables

Let a lambda use a value from the surrounding scope.

capture A lambda can read nearby variables without receiving them as parameters.

Capturing Variables

offset
CapturingVariables.kt
Replay: real traced execution (multi-file project)
fun applyToBase(base: Int, change: (Int) -> Int): Int {
    val updated = change(base)
    return updated
}

fun main() {
    val offset = 2
    val result = applyToBase(10) { value ->
        value + offset
    }

    println("offset=$offset")
    println("result=$result")
}

fun applyToBase(base: Int, change: (Int) -> Int): Int {
    val updated = change(base)
    return updated
}

fun main() {
    val offset = 0
    val result = applyToBase(10) { value ->
        value + offset
    }

    println("offset=$offset")
    println("result=$result")
}

fun applyToBase(base: Int, change: (Int) -> Int): Int {
    val updated = change(base)
    return updated
}

fun main() {
    val offset = 5
    val result = applyToBase(10) { value ->
        value + offset
    }

    println("offset=$offset")
    println("result=$result")
}

  1. offset ← 2

    6fun main() {7    val offset→ 2 = 2 //@offset=0, 58    val result = applyToBase(10) { value ->9        value + offset10    }

  2. updated ← 12

    1fun applyToBase(base10: Int, change: (Int) -> Int): Int {2    val updated→ 12 = change(base10)3    return updated124}

  3. result ← 12

    7    val offset = 2 //@offset=0, 58    val result→ 12 = applyToBase(10) { value ->9        value + offset10    }1112    println("offset=$offset2")13    println("result=$result12")14}
    outputoffset=2
result=12

  1. offset ← 0

    6fun main() {7    val offset→ 0 = 08    val result = applyToBase(10) { value ->9        value + offset10    }

  2. updated ← 10

    1fun applyToBase(base10: Int, change: (Int) -> Int): Int {2    val updated→ 10 = change(base10)3    return updated104}

  3. result ← 10

    7    val offset = 08    val result→ 10 = applyToBase(10) { value ->9        value + offset10    }1112    println("offset=$offset0")13    println("result=$result10")14}
    outputoffset=0
result=10

  1. offset ← 5

    6fun main() {7    val offset→ 5 = 58    val result = applyToBase(10) { value ->9        value + offset10    }

  2. updated ← 15

    1fun applyToBase(base10: Int, change: (Int) -> Int): Int {2    val updated→ 15 = change(base10)3    return updated154}

  3. result ← 15

    7    val offset = 58    val result→ 15 = applyToBase(10) { value ->9        value + offset10    }1112    println("offset=$offset5")13    println("result=$result15")14}
    outputoffset=5
result=15