BitSet

UpdatedOct 1, 2026

BitSet

import { BitSet } from "@alloy/std/collections"

local visited = new BitSet(1024)
visited:add(7):add(40)
if visited:has(7) then end
for i in visited do print(i) end

A set of whole numbers from 0 up, from the std, with one bit per number in a buffer. A Set<number> spends a table slot on each member. A BitSet spends one bit on each number up to its largest member, and add and has run about 2x faster. It suits dense numbers: tile indices, entity ids, visited flags. new BitSet(size) makes room for the numbers below size, and a larger number grows the buffer. for i in bits walks the members in rising order.

Statics

BitSet.new

BitSet.new(size: number?): BitSet

An empty set with room for the numbers below size, or below 256 without it. A larger number grows the buffer, so size only saves the copies.

import { BitSet } from "@alloy/std/collections"

local visited = new BitSet(1024)
visited:add(7)

BitSet.from

BitSet.from(indices: { number }): BitSet

A new set of the numbers in an array. A repeated number joins once.

import { BitSet } from "@alloy/std/collections"

local bits = BitSet.from({ 1, 2, 2, 9 })
print(bits:len())

Methods

BitSet:add

BitSet:add(index: number): BitSet

Adds index and returns the set, so calls chain. The number must be whole and 0 or more, or the call raises.

import { BitSet } from "@alloy/std/collections"

local bits = new BitSet()
bits:add(3):add(5)
print(bits:has(5))

BitSet:has

BitSet:has(index: number): boolean

Whether index is a member. A number below 0, past the buffer, or with a fraction is not one.

import { BitSet } from "@alloy/std/collections"

local bits = BitSet.from({ 4 })
print(bits:has(4))

BitSet:remove

BitSet:remove(index: number): boolean

Removes index and says whether it was there.

import { BitSet } from "@alloy/std/collections"

local bits = BitSet.from({ 4 })
print(bits:remove(4))

BitSet:len

BitSet:len(): number

The number of members. The set counts as members come and go, so this costs the same at any size.

import { BitSet } from "@alloy/std/collections"

local bits = BitSet.from({ 1, 2, 3 })
print(bits:len())

BitSet:is_empty

BitSet:is_empty(): boolean

Whether the set holds no members.

import { BitSet } from "@alloy/std/collections"

local bits = new BitSet()
print(bits:is_empty())

BitSet:clear

BitSet:clear()

Removes every member. The buffer keeps its size.

import { BitSet } from "@alloy/std/collections"

local bits = BitSet.from({ 1, 2 })
bits:clear()

BitSet:union

BitSet:union(other: BitSet): BitSet

A new set of the members of both, built 32 bits at a time. Neither input changes.

import { BitSet } from "@alloy/std/collections"

local a = BitSet.from({ 1, 2 })
local b = BitSet.from({ 2, 3 })
print(a:union(b):len())

BitSet:intersection

BitSet:intersection(other: BitSet): BitSet

A new set of the members that both hold.

import { BitSet } from "@alloy/std/collections"

local a = BitSet.from({ 1, 2 })
local b = BitSet.from({ 2, 3 })
print(a:intersection(b):len())

BitSet:difference

BitSet:difference(other: BitSet): BitSet

A new set of this set's members that other does not hold.

import { BitSet } from "@alloy/std/collections"

local a = BitSet.from({ 1, 2 })
local b = BitSet.from({ 2, 3 })
print(a:difference(b):len())

BitSet:to_array

BitSet:to_array(): number[]

The members as an array, in rising order.

import { BitSet } from "@alloy/std/collections"

local bits = BitSet.from({ 9, 2 })
print(bits:to_array():join(", "))