Random

Standard library class · Made with Random(seed)

A Random makes random choices that you can repeat. Give two of them the same seed, ask them the same things in the same order, and they give the same answers. That is what a test needs, so its result is the same on every run, and what a game needs to replay a level exactly.

const first = Random(42)
const second = Random(42)
print(first.next(1..6) == second.next(1..6))   # → true

For everyday randomness, where each run should differ, you don’t need one: use the built-in random(range), and a list’s own random() and shuffle().

The seed decides the results only within one version of Emerald. A later version may give different numbers for the same seed, so don’t save them expecting to get the same ones back.

At a glance

Making one
`Random(seed)`	A generator starting from `seed`

Choosing
`next(range)`	A whole number from a range
`choose(list)`	One item from a list, or `nothing` if it is empty
`shuffle!(list)`	Shuffle a list in place

Making one

Random(seed: Int): Random

A generator starting from seed. Any whole number works; what matters is using the same one when you want the same results.

const dice = Random(7)

Choosing

next(range: Range): Int

One whole number from range, as the built-in random(range) chooses, but repeatably. The range’s ends decide what is possible: next(1..6) can give 6, but next(0..<10) can never give 10.

const dice = Random(7)
const roll = dice.next(1..6)
print(roll.between?(1, 6))   # → true

Raises when range is empty.

choose(list: List[T]): T?

One item from list, or nothing when the list is empty. The result is optional, so give it a fallback with or or check it before using it.

const picker = Random(1)
const move = picker.choose(["rock", "paper", "scissors"]).or("rock")

const nobody: List[String] = []
print(picker.choose(nobody))   # → nothing

shuffle!(list: List[T])

Puts the items of list in a random order, changing the list itself. Every item stays in it exactly as many times as before. The list must be a var, since it changes.

const cards = Random(3)
var deck = [1, 2, 3, 4, 5]
cards.shuffle!(deck)
print(deck.count)   # → 5