Collections vs Sequences

CollectionsVsSequences.kt

var someNumbers = listOf(1, 4, 5, 6, 7, 8, 2323, 5456, 343, 2)
someNumbers
    .filter { it % 2 == 0 } 
    .map { it * 3 } 
    .sum()

someNumbers
    .asSequence()
    .filter { it % 2 == 0 }
    .map { it * 2 }
    .sum()

// collection
interface Iterable<out T> {
    operator fun iterator(): Iterator<T>
}

// sequence
interface Sequence<out T> {
    operator fun iterator(): Iterator<T>
}

// collection
public inline fun <T, R> Iterable<T>.map(transform: (T) -> R): List<R> {
    return mapTo(ArrayList<R>(collectionSizeOrDefault(10)), transform)
}

// sequence
public fun <T, R> Sequence<T>.map(transform: (T) -> R): Sequence<R> {
    return TransformingSequence(this, transform)
}

var someNumbers = listOf(1, 4, 5, 6, 7, 8, 2323, 5456, 343, 2)
someNumbers
    .filter { it % 2 == 0 } // 1 collection created
    .map { it * 3 } // 1 collection created
    .sum()
// total collections created = 2 

someNumbers
    .asSequence()
    .filter { it % 2 == 0 }
    .map { it * 2 }
    .sum() 
// total collections created = 0