How to lazily evaluate collections in Scala

Knoldus Blogs

The Scala language provides to ways to implement the collections. One is strict and other is non-strict or lazy.

Whenever, the instance of a collection (except for the Streams) is created, it creates the strict version of the collection which means memory is allocated at the same time.

A simple example of strict collection is:

val list = List(1,2,3,4,5,6,7,8,9,10)
list: List[Int] = List(1, 2, 3, 4, 5, 6, 7, 8, 9, 10)

The above code, the memory would be allocated for the List immediately.

But whenever a view in the collection is created, it makes that collection as a lazy collection which means memory allocation would not be done at the time of initialization, instead, it would take place whenever they are actually accessed or some transformations are applied on them.

For example,

val listView = List(1,2,3,4,5,6,7,8,9,10).view
listView: scala.collection.SeqView[Int,List[Int]] = SeqView(...)

Here, the type of listView is SeqView[Int, List[Int]]

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