CODEWITHSUNDEEP
scalafunctional-programmingscala-2.11
Lasf
Lasf

Reputation: 2582

How easy is lazy evaluation by converting a non-lazy collection to a stream?

This might be a silly question, but I've been unsure of it for a while. Let's assume this iterates over our list three times:

def doSomething(list: List[Int]): List[Int] =
  list.map(...).flatMap(...).map(...)

If I instead do:

def doSomething(list: List[Int]): List[Int] =
  list.toStream.map(...).flatMap(...).map(...).toList

Am I guaranteed a single iteration?

Upvotes: 3

Views: 219

Answers (1)

ntn
ntn

Reputation: 1177

As far as I know, converting to .toStream should do the iteration only once.
Though, the more standard way of doing this is using .view and then .force at the end

def doSomething(list: List[Int]): List[Int] =
  list.view.map(...).flatMap(...).map(...).force

Using .view on a collection returns a lazy version of it, and calling .force on the lazy view creates the collection.

Upvotes: 5

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