Sequences in kotlin

Background

• There are many ways to handle a group of items.
• Collections and Sequences provide many utilities.
• Eagerly with the collections and Lazily with sequences.

Difference b/w Eagerly and Lazy

• Depends on when the transformation is performed on the collection

Collection use Eagerly

• On each operation, A new collection is formed and modified based on the operator's nature.
• Operations on the collections are implemented using inline functions.
• Collection creates a new list for each operation.

Sequences use Lazily

• Sequence is created based on the iterator of the original collection.
• So we need to add asSequence()
• The operations are added to the list of operations to be performed but the operations are not performed immediately
• Instead, the Terminal operator is applied first if it contains it, and thus map is not applied if it contains it.
• Also new copy is not created on each operator invocation.
• Each operation is not an inline function.
• Sequence creates a new object for every operation

Performance comparison on collection and sequence

• Whether you use collection or sequence, The order of operators matters.
• When used with small data collections or sequences does not matter.
• When used with large data, The sequence is the better choice.

Example Demo

data class Shape(val name:String , var color: String)

val listOfShapes = listOf(
    Shape(name = "Circle", color = "Green"),
    Shape(name = "Rectangle", color = "Purple"),
    Shape(name = "Triangle", color = "Red"),
    Shape(name = "Triangle", color = "Yellow")
)

fun main(args: Array<String>) {

    val shapesWithYellowColor = listOfShapes
        // Convert the color to yellow
        .map {
            it.copy(color = "Yellow")
        }
        // Pick the first rectangle
        .first{
            it.name == "Rectangle"
        }


    val shapesWithRedColor = listOfShapes.asSequence()
        // Convert the color to yellow
        .map {
            it.copy(color = "Red")
        }
        // Pick the first rectangle
        .first{
            it.name == "Triangle"
        }

}