In Scala, what does “view” do?

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View produces a lazy collection, so that calls to e.g. filter do not evaluate every element of the collection. Elements are only evaluated once they are explicitly accessed. Now sum does access all elements, but with view the call to filter doesn’t create a full Vector. (See comment by Steve)

A good example of the use of view would be:

scala> (1 to 1000000000).filter(_ % 2 == 0).take(10).toList
java.lang.OutOfMemoryError: GC overhead limit exceeded

Here Scala tries to create a collection with 1000000000 elements to then access the first 10. But with view:

scala> (1 to 1000000000).view.filter(_ % 2 == 0).take(10).toList
res2: List[Int] = List(2, 4, 6, 8, 10, 12, 14, 16, 18, 20)

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