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scalastreamlazy-evaluationmemoizationscala-streams

Scala how to get last calculated value of stream?

According to scala docs stream implements lazy lists where elements are only evaluated when they are needed. Example;

val fibs: Stream[BigInt] = BigInt(0) #:: BigInt(1) #:: fibs.zip(fibs.tail).map(n => { 
    n._1 + n._2
})

After that in scala repl;

fibs(4)
fibs

It will print out;

res1: Stream[BigInt] = Stream(0, 1, 1, 2, 3, ?)

Since calling .length or .last causes infinite loop,how can I get value "3" (last calculated value) in most efficient way?

Solution

  • You cannot. This is not part of the API of Stream. And with reason, because that would allow you to observe a value that changes over time from a Stream, and that violate the (lazy) immutable nature of Stream.