Standard Library Utilities

Collection Helpers

Use collection helpers to transform and summarize a short list.

collection-helpers Small helpers such as `map`, `filter`, and `joinToString` make collection steps readable.

Collection Helpers

bonus
CollectionHelpers.kt
Replay: real traced execution (multi-file project)
fun main() {
    val bonus = 2
    val scores = listOf(1, 3, 5)
    val adjusted = scores.map { score ->
        score + bonus
    }
    val high = adjusted.filter { score ->
        score >= 5
    }
    val summary = high.joinToString("-")

    println("bonus=$bonus")
    println("count=${high.size}")
    println("summary=$summary")
}

fun main() {
    val bonus = 0
    val scores = listOf(1, 3, 5)
    val adjusted = scores.map { score ->
        score + bonus
    }
    val high = adjusted.filter { score ->
        score >= 5
    }
    val summary = high.joinToString("-")

    println("bonus=$bonus")
    println("count=${high.size}")
    println("summary=$summary")
}

fun main() {
    val bonus = 5
    val scores = listOf(1, 3, 5)
    val adjusted = scores.map { score ->
        score + bonus
    }
    val high = adjusted.filter { score ->
        score >= 5
    }
    val summary = high.joinToString("-")

    println("bonus=$bonus")
    println("count=${high.size}")
    println("summary=$summary")
}

  1. bonus ← 2, scores ← [1, 3, 5], adjusted ← [3, 5, 7], high ← [5, 7]

    1fun main() {2    val bonus→ 2 = 2 //@bonus=0, 53    val scores→ [1, 3, 5] = listOf(1, 3, 5)4    val adjusted→ [3, 5, 7] = scores[1, 3, 5].map { score ->5        score + bonus6    }7    val high→ [5, 7] = adjusted[3, 5, 7].filter { score ->8        score >= 59    }10    val summary→ 5-7 = high[5, 7].joinToString("-")1112    println("bonus=$bonus2")13    println("count=${high.size2}")14    println("summary=$summary5-7")15}
    outputbonus=2
count=2
summary=5-7

  1. bonus ← 0, scores ← [1, 3, 5], adjusted ← [1, 3, 5], high ← [5]

    1fun main() {2    val bonus→ 0 = 03    val scores→ [1, 3, 5] = listOf(1, 3, 5)4    val adjusted→ [1, 3, 5] = scores[1, 3, 5].map { score ->5        score + bonus6    }7    val high→ [5] = adjusted[1, 3, 5].filter { score ->8        score >= 59    }10    val summary→ 5 = high[5].joinToString("-")1112    println("bonus=$bonus0")13    println("count=${high.size1}")14    println("summary=$summary5")15}
    outputbonus=0
count=1
summary=5

  1. bonus ← 5, scores ← [1, 3, 5], adjusted ← [6, 8, 10], high ← [6, 8, 10]

    1fun main() {2    val bonus→ 5 = 53    val scores→ [1, 3, 5] = listOf(1, 3, 5)4    val adjusted→ [6, 8, 10] = scores[1, 3, 5].map { score ->5        score + bonus6    }7    val high→ [6, 8, 10] = adjusted[6, 8, 10].filter { score ->8        score >= 59    }10    val summary→ 6-8-10 = high[6, 8, 10].joinToString("-")1112    println("bonus=$bonus5")13    println("count=${high.size3}")14    println("summary=$summary6-8-10")15}
    outputbonus=5
count=3
summary=6-8-10