`Sequence` is lazy

# announcements

[Leon K]

Sequence is lazy

[Matej Drobnič]

Aren't iterators also lazy?

[Fleshgrinder]

They are and sequences are iterators. The difference is that sequences are suspendable.

[Leon K]

from the kotlin doc:
"
Along with collections, the Kotlin standard library contains another container type – sequences (Sequence<T>). Sequences offer the same functions as Iterable but implement another approach to multi-step collection processing.

When the processing of an Iterable includes multiple steps, they are executed eagerly: each processing step completes and returns its result – an intermediate collection. The following step executes on this collection. In turn, multi-step processing of sequences is executed lazily when possible: actual computing happens only when the result of the whole processing chain is requested.
"
-> https://kotlinlang.org/docs/reference/sequences.html

[Fleshgrinder]

Proof https://github.com/JetBrains/kotlin/blob/e8524137c3350276956e9854eadc8bd60bc291d7/libraries/stdlib/src/kotlin/collections/Sequences.kt#L125

[Leon K]

with lazy i meant lazy in the way they apply and calculate transformations
pretty sure normal iterators don't do it the same "lazy" way that sequences do

[Matej Drobnič]

You described difference between Sequence and Iterable

[Matej Drobnič]

not between Sequence and Iterator

[Leon K]

that might be my mistake, yes

[Leon K]

sorry in that case

[Fleshgrinder]

An iterator can be anything, in Rust all iterators are by default lazy. That was not possible in Kotlin because they are backed by Java and Java iterators are mostly eager. It's an implementation detail.

[Leon K]

yea, i just confused Iterator<T> with Iterable<T> 😕