```operator fun Body iterator Iterator lt Body gt val body = kotlinlang #getting-started

operator fun Body.iterator(): Iterator<Body> {
    val body = this
    return object : Iterator<Body> {
        var current: Body? = body

        override fun hasNext(): Boolean {
            return current != null
        }

        override fun next(): Body {
            val result = current!!
            current = result.getNext()
            return result
        }
    }
}

Chris Lee

06/03/2022, 3:15 PM

s/b

this@iterator

or similar to get you back to the enclosing method.

mkrussel

06/03/2022, 3:19 PM

The

next

function is throwing the wrong exception based on the contract from Java. Kotlin has no contract on what to do if

next

cannot return anything.

Joffrey

06/03/2022, 3:21 PM

Yeah I would suggest adapting to a

Sequence

instead, so you don't have to deal with the iterator interface yourself

Something like this:

fun Body.asSequence(): Sequence<Body> = sequence {
    var current: Body? = this@asSequence
    while(current != null) {
        yield(current)
        current = current.getNext()
    }
}

https://pl.kotl.in/Uk-KSmcQL

Jonathan Ellis

06/03/2022, 5:15 PM

@Joffrey thanks. the reason I like iterator is that a for loop knows how to apply the iterator operator automatically. with the sequence approach I'd have to call .asSequence explicitly right?

Joffrey

06/03/2022, 5:21 PM

That's right. It's a fair point. You could of course implement the

iterator()

operator with

asSequence().iterator()

but you may as well just implement it directly like you just did.

✅ 1

Sam

06/06/2022, 7:41 AM

There's also an

iterator { ... }

builder that works exactly like the

sequence { ... }

builder.

😯 1

Joffrey

06/06/2022, 8:00 AM

TIL

Sam

06/06/2022, 8:07 AM

It's funny that it's not more well-known! Especially since the implementation of

sequence { ... }

is just

= Sequence { iterator(block) }

It never seems to be mentioned in the docs. Maybe iterators just aren't cool these days 😄.

Joffrey

06/06/2022, 8:59 AM

To be fair I rarely use

for

loops, so I rarely implement the

iterator

operator. And mutating a list while iterating is something I haven't had to use in Kotlin at all (for years), and this was the main reason to use iterators directly

So I get the "iterators are not cool anymore" part :)

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