New Features in Ruby 3.0.0 Preview 1: RBS, Ractor, and Scheduler

Ruby 3.0.0 Preview 1 has been released, bringing several new features to the language.

RBS is a language for describing Ruby program types. It enables type checkers and other tools to understand class and module definitions, method signatures, instance variables, inheritance, mixins, and supports advanced types such as unions, method overloads, generics, and duck‑typing interfaces.

Ruby 3.0 ships with the rbs gem that can parse and handle RBS type definitions. An example definition:

module ChatApp
  VERSION: String

  class Channel
    attr_reader name: String
    attr_reader messages: Array[Message]
    attr_reader users: Array[User | Bot]  # `|` means union types, User or Bot.

    def initialize: (String) -> void

    def post: (String, from: User | Bot) -> Message  # Method overloading is supported.
                | (File, from: User | Bot) -> Message
  end
end

Ractor (experimental) is an actor‑model concurrency abstraction that provides parallel execution without thread‑safety concerns. The following code runs two Ractors in parallel to compute prime? , roughly doubling speed:

require 'prime'

# n.prime? with sent integers in r1, r2 run in parallel
r1, r2 = *(1..2).map do
  Ractor.new do
    n = Ractor.recv
    n.prime?
  end
end

# send parameters
r1.send 2**61 - 1
r2.send 2**61 + 15

# wait for the results of expr1, expr2
p r1.take #=> true
p r2.take #=> true

Scheduler (experimental) introduces Thread#scheduler to intercept blocking operations, allowing lightweight concurrency without changing existing code. Currently supported classes/methods include:

Mutex#lock , Mutex#unlock , Mutex#sleep

ConditionVariable#wait

Queue#pop , SizedQueue#push

Thread#join

Kernel#sleep

IO#wait , IO#read , IO#write and related methods such as #wait_readable , #gets , #puts

Not supported: IO#select

For more details, see the official release notes: Ruby 3.0.0 Preview 1 released .