std.iter

Functional helpers on arrays. Array-in, array-out — there’s no lazy iterator protocol. If you care about allocation, a hand-written for loop will always beat these.

Every helper handles empty arrays gracefully and preserves relative order.

Import

use std.iter                                // glob
use std.iter.{map, filter, reduce}          // selective
use std.iter as i                           // aliased

Higher-order

map(arr, f)

Apply f to each element; return a new array of results.

use std.iter.{map}
print(map([1, 2, 3], fn(x) { return x * 2 }))     // [2, 4, 6]

filter(arr, pred)

Keep only the elements for which pred(x) is truthy.

use std.iter.{filter}
let evens = filter([1, 2, 3, 4, 5], fn(n) { return n % 2 == 0 })
print(evens)    // [2, 4]

reduce(arr, initial, combine)

Fold over the array left-to-right with a two-arg combiner.

use std.iter.{reduce}
let sum = reduce([1, 2, 3, 4], 0, fn(acc, x) { return acc + x })
print(sum)    // 10

all(arr, pred), any(arr, pred)

all returns true when every element passes (vacuously true for empty). any returns true when at least one element passes.

use std.iter.{all, any}
print(all([2, 4, 6], fn(n) { return n % 2 == 0 }))    // true
print(any([1, 3, 4], fn(n) { return n % 2 == 0 }))    // true

count(arr, pred)

Count elements for which pred(x) is truthy.

use std.iter.{count}
print(count([1, 2, 3, 4, 5], fn(n) { return n > 2 }))   // 3

find(arr, pred) / find_index(arr, pred)

find returns the first matching element, or none if no match. find_index returns the 0-based index, or -1.

use std.iter.{find, find_index}
print(find([1, 2, 3, 4], fn(n) { return n > 2 }))          // 3
print(find_index([1, 2, 3, 4], fn(n) { return n > 2 }))    // 2

Slicing

take(arr, n)

First n elements (or the whole array if it’s shorter). Negative n yields an empty array.

use std.iter.{take}
print(take([1, 2, 3, 4, 5], 3))    // [1, 2, 3]
print(take([1, 2], 10))            // [1, 2]

drop(arr, n)

Drop the first n elements. Negative n yields a full copy; n >= arr.len() yields [].

use std.iter.{drop}
print(drop([1, 2, 3, 4, 5], 2))    // [3, 4, 5]

Combining

zip(a, b)

Pair elements from two arrays. Stops at the shorter array’s length.

use std.iter.{zip}
print(zip([1, 2, 3], ["a", "b", "c"]))    // [[1, "a"], [2, "b"], [3, "c"]]

enumerate(arr)

Pair each element with its 0-based index.

use std.iter.{enumerate}
print(enumerate(["a", "b"]))    // [[0, "a"], [1, "b"]]

flatten(arr)

Flatten an array of arrays one level down.

use std.iter.{flatten}
print(flatten([[1, 2], [3, 4], [5]]))    // [1, 2, 3, 4, 5]

Reductions

sum(arr)

Sum of a numeric array. Empty → 0.

use std.iter.{sum}
print(sum([1, 2, 3, 4]))     // 10
print(sum([]))               // 0

product(arr)

Product of a numeric array. Empty → 1 (multiplicative identity, matching NumPy / Python’s math.prod).

use std.iter.{product}
print(product([2, 3, 4]))    // 24
print(product([]))           // 1

min_array(arr) / max_array(arr)

Minimum / maximum of a numeric array. Raises on empty input so callers notice.

use std.iter.{min_array, max_array}
print(min_array([3, 1, 4, 1, 5]))    // 1
print(max_array([3, 1, 4, 1, 5]))    // 5

For pairwise min / max use the .min() / .max() numeric methods instead.