Can someone explain to me, why hashCode is different for these `s1`, `s2` sequences? I would expect ...

# getting-started

[Natalia Peterwas]

Can someone explain to me, why hashCode is different for these s1, s2 sequences? I would expect it to be the same as in lists.

// 1
    val s1 = sequenceOf(1, 2, 3)
    val s2 = sequenceOf(1, 2, 3)
    s1.hashCode() == s2.hashCode() // false - why?
    
    // 2
    val l1 = sequenceOf(1, 2, 3).toList()
    val l2 = sequenceOf(1, 2, 3).toList()
    l1.hashCode() == l2.hashCode() // true - fine as lists contain the same items

[ephemient]

sequence is an abstraction over iterator. it is not expected to be a persistent collection - use collection for that

[CLOVIS]

Sequences cannot go through their elements (what if the sequence was infinite?), so the hash cannot depend on the elements.

[ephemient]

even if it out were finite, a sequence may be iterable only once. so again the hash code can't use the elements

[Natalia Peterwas]

@ephemient can you please elaborate on the last answer?

[Natalia Peterwas]

Don’t I iterate twice over the same sequence here 🤔

val s1 = sequenceOf(1, 2, 3)
    s1.forEach { println(it) }
    s1.forEach { println(it) }

[ephemient]

some sequences, not all

[ephemient]

var i = 0
val s = generateSequence { ++i }.take(3)
s.forEach {}
s.forEach {}

throws

[ephemient]

as does

listOf(1, 2, 3).iterator().asSequence()

that's basically the difference between Iterable and Sequence. the interface is similar but the expectations are different