array_utils tutorial

This tutorial walks through the array helpers with small examples taken from the doc comments and tests in src. To use them in your own module, add the dependency with moon add Luna-Flow/luna-utils and import the package Luna-Flow/luna-utils; the functions are then available as @luna-utils.arr_sum and so on. The examples below run inside the package and omit the prefix.

Sums

arr_sum works for any element type with an additive monoid, and zero_arr creates an array of zeros of the expected type:

inspect(arr_sum([1, 2, 3, 4]), content="10")
let empty : Array[Int] = []
inspect(arr_sum(empty), content="0")
inspect(arr_abs_sum([1, -2, 3, -4, 5]), content="15")
let zeros : Array[Double] = zero_arr(3)
assert_eq(zeros, [0.0, 0.0, 0.0])

Extremes and search

let xs = [5, 2, 8, 1, 9]
inspect(arr_max(xs), content="9")
inspect(arr_min(xs), content="1")
inspect(find([1, 2, 3, 2, 4], 2), content="Some(1)")
inspect(find([1, 2, 3, 2, 4], 5), content="None")

arr_max and arr_min panic on an empty array, so check xs.is_empty() first when the array may be empty.

Reversing

reverse returns a new array, while reverse_inplace changes its argument:

let original = [1, 2, 3, 4, 5]
inspect(reverse(original), content="[5, 4, 3, 2, 1]")
inspect(original, content="[1, 2, 3, 4, 5]")
reverse_inplace(original)
inspect(original, content="[5, 4, 3, 2, 1]")

Checking uniformity

same and same_to compare the elements themselves; map_same and map_same_to compare their images under a function:

inspect(same([1, 1, 1, 1]), content="true")
inspect(same_to([1, 2, 1, 1], 1), content="false")
inspect(map_same([2, 4, 6, 8], x => x % 2), content="true")
inspect(map_same_to([1, 1, 1], 2, x => x * 2), content="true")

same and map_same panic on an empty array. When the array may be empty and you know the expected value, use same_to or map_same_to, which return true for an empty array.

Next steps

The API reference gives every signature, and the design notes explain the constraints and the treatment of empty arrays. Before relying on edge-case behaviour, check it against the tests in src/array_utils_test.mbt.