Arrays

Literal, indexing, push/pop, slicing, spread, and functional operations.

// Feature: Arrays — 0-indexed ordered collection

// Syntax: `[a, b, c]`, indexing `arr[i]`, slicing `arr[i..j]`

// When to use: list of N values accessible by position, order

// matters, frequent append/pop.


use std::Array

// Literal and 0-based indexing.

let nums = [10, 20, 30, 40, 50]
print(nums[0])  // 10

print(nums[4])  // 50

print(nums.len())  // 5


// Type inferred as `[int]`. Explicit annotation:

let names: [str] = ["Alice", "Bob", "Carol"]
print(names[1])  // Bob


// Mutability: `let mut` + `Array.push/pop` or `.push()`.

let mut bag = [1, 2, 3]
bag.push(4)
bag.push(5)
print(bag)  // [1, 2, 3, 4, 5]


let last = bag.pop()
print(last)  // 5

print(bag)  // [1, 2, 3, 4]


// Slicing by range — creates a new array.

let s = nums[0..3]  // [10, 20, 30]   exclusive

let t = nums[2..=4]  // [30, 40, 50]   inclusive

print(s)
print(t)

// Spread in literals.

let a = [1, 2]
let b = [3, 4]
let merged = [0, ...a, ...b, 5]
print(merged)  // [0, 1, 2, 3, 4, 5]


// Functional operations (see also 05-functions/06-higher-order).

let doubled = Array::map([1, 2, 3], |x| x * 2)
let evens = Array::filter([1, 2, 3, 4], |x| x % 2 == 0)
let total = Array::reduce([1, 2, 3, 4], |acc, x| acc + x, 0)
print(doubled)  // [2, 4, 6]

print(evens)  // [2, 4]

print(total)  // 10


// Sort and reverse — return a new array.

let desc = Array::sort([3, 1, 4, 1, 5, 9, 2]).reverse()
print(desc)  // [9, 5, 4, 3, 2, 1, 1]