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feat(iter): add iteri and iter2 #2012

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feat(iter): add iteri and iter2 #2012

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2 changes: 2 additions & 0 deletions builtin/builtin.mbti
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Original file line number Diff line number Diff line change
Expand Up @@ -236,6 +236,8 @@ impl Iter {
head[A](Self[A]) -> A?
intersperse[A](Self[A], A) -> Self[A]
iter[T](Self[T]) -> Self[T]
iter2[K, V](Self[(K, V)]) -> Iter2[K, V]
iteri[T](Self[T], offset~ : Int = ..) -> Iter2[Int, T]
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@bobzhang bobzhang Apr 28, 2025 •
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iteri looks reasonable.
What's the benefit of having iter2, it doe not have perf benefit either?

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We don't have pattern matching for for .. in, so one would have to write:

let map = [("a", "b"), ("c", "d")].iter()
for v in map {
  let (k, v) = v
}

With iter2, one can at least write:

for k, v in map.iter2() {
}

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We will use iter2 -> Iter2[Int, T]

join(Self[String], String) -> String
just_run[T](Self[T], (T) -> IterResult) -> Unit
last[A](Self[A]) -> A?
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20 changes: 20 additions & 0 deletions builtin/iter.mbt
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Expand Up @@ -968,3 +968,23 @@ pub fn Iter::minimum[T : Compare](self : Iter[T]) -> T? {
}
res
}

///|
/// Returns an iterator that iterates over the index and the element of the iterator.
pub fn Iter::iteri[T](self : Iter[T], offset~ : Int = 0) -> Iter2[Int, T] {
fn {
yield_ => {
let mut value = offset - 1
self.run(fn(i) {
value += 1
yield_(value, i)
})
}
}
}

///|
/// Returns an iterator that iterates over the key value pair.
pub fn Iter::iter2[K, V](self : Iter[(K, V)]) -> Iter2[K, V] {
fn { yield_ => self.run(fn { (k, v) => yield_(k, v) }) }
}
28 changes: 28 additions & 0 deletions builtin/iter_test.mbt
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Expand Up @@ -748,3 +748,31 @@ test "Float::until negative step" {
let result = 10.0.until(0.0, step=-2.0).collect()
inspect!(result, content="[10, 8, 6, 4, 2]")
}

///|
test "iteri" {
let iter = [].iter()
for _, _ in iter.iteri() {
assert_true!(false)
}
let iter = [0, 1, 2].iter()
for i, x in iter.iteri() {
assert_eq!(i, x)
}
let iter = [0, 1, 2].iter()
for i, x in iter.iteri(offset=10) {
assert_eq!(i, x + 10)
}
}

///|
test "iter2" {
let iter = [].iter()
for _, _ in iter.iter2() {
assert_true!(false)
}
let iter = [(0, 1), (2, 3), (4, 5)].iter()
for k, v in iter.iter2() {
assert_eq!(k + 1, v)
}
}