What's New in Ruby 3.5 Preview

20 Jul 2025 · 5 min read

Ruby 3.5.0 preview1 was released on April 18, 2025. While this is just a preview release and not recommended for production use, it gives us a glimpse of what’s coming in the final Ruby 3.5 release.

Set Becomes a Core Class

Ruby 3.5 promotes Set from a stdlib class to a core class. Previously, Set was implemented in Ruby using Hash internally. The new core implementation is written in C and uses a custom hash table structure optimized for Set operations, which stores only keys without the unnecessary values that Hash requires.

# No functional changes for users
set = Set.new([1, 2, 3])
set.add(4)
set.include?(2)  # => true

This change brings performance improvements for most Set operations and reduces memory usage by about 33% for large sets.

Ractor Gets Major Updates with Ractor::Port

Ruby 3.5 introduces Ractor::Port for better synchronization between Ractors, while removing several existing methods.

New Ractor::Port

# Create a port for communication
port = Ractor::Port.new

# Producer Ractor sends data through the port
producer = Ractor.new(port) do |port|
  5.times do |i|
    data = { id: i, value: i * 10 }
    port.send(data)
    sleep(0.1)
  end
  port.send(:done)
end

# Consumer Ractor receives data from the port
consumer = Ractor.new(port) do |port|
  loop do
    msg = port.recv
    break if msg == :done
    puts "Received: #{msg}"
  end
end

# Wait for both to complete
producer.join
consumer.join

Removed Ractor Methods

The following methods have been removed:

Ractor.yield
Ractor#take
Ractor.select
Ractor#close_incoming
Ractor#close_outgoing

Migrating from Old Ractor API

If you have existing code using Ractor.yield and take, here’s how to migrate:

Before (Ruby 3.4)

# Worker Ractor that yields results
worker = Ractor.new do
  10.times do |i|
    result = i ** 2
    Ractor.yield(result)  # Send result to parent
  end
end

# Main Ractor takes results
10.times do
  value = worker.take  # Receive from worker
  puts "Got: #{value}"
end

After (Ruby 3.5)

# Create a port for communication
port = Ractor::Port.new

# Worker Ractor sends through port
worker = Ractor.new(port) do |port|
  10.times do |i|
    result = i ** 2
    port.send(result)  # Send result through port
  end
end

# Main thread receives from port
10.times do
  value = port.recv  # Receive from port
  puts "Got: #{value}"
end

Developer Action Required: Replace Ractor.yield with port.send and ractor.take with port.recv using the new Ractor::Port API.

Simplified nil Splat Behavior

Ruby 3.5 makes splat operator behavior with nil more consistent.

Before Ruby 3.5

def process(*args)
  p args
end

# This would call nil.to_a internally
process(*nil)  # => []

Ruby 3.5

def process(*args)
  p args
end

# No longer calls nil.to_a
process(*nil)  # => []

# Consistent with double splat
def options(**opts)
  p opts
end

options(**nil)  # => {} (already worked this way)

IO.select Gets Infinity Support

IO.select now accepts Float::INFINITY as a timeout argument for cases where you want to wait indefinitely.

# Wait forever for IO to be ready
ready = IO.select([socket], nil, nil, Float::INFINITY)

Binding Changes for Numbered Parameters

Numbered parameters (_1, _2, etc.) are no longer included in binding introspection.

[1, 2, 3].map { binding.local_variables }
# Before: [:_1]
# Ruby 3.5: []

[1, 2, 3].map { binding.local_variable_get(:_1) }
# Ruby 3.5: raises NameError

This change makes numbered parameters truly anonymous. If you’re using numbered parameters, consider migrating to the cleaner it parameter introduced in Ruby 3.4:

# Instead of numbered parameters
users.map { _1.name }

# Use the it parameter
users.map { it.name }

Custom Inspect with instance_variables_to_inspect

Kernel#inspect now supports customizing which instance variables are shown.

class User
  def initialize
    @id = 1
    @password = "secret"
    @email = "user@example.com"
  end

  def instance_variables_to_inspect
    [:@id, :@email]  # Don't show @password
  end
end

User.new.inspect
# => #<User:0x... @id=1, @email="user@example.com">

Socket Gets Connection Timeout

Socket.tcp adds an open_timeout keyword argument for connection timeouts.

# Timeout connection attempt after 5 seconds
Socket.tcp("example.com", 80, open_timeout: 5) do |socket|
  socket.puts "GET / HTTP/1.0\r\n\r\n"
  puts socket.read
end

Default Gems Updates

Several gems have been updated to newer versions as default gems:

ostruct 0.6.2
pstore 0.2.0
benchmark 0.4.1
logger 1.7.0

These are bundled with Ruby, so you don’t need to add them to your Gemfile.

Important Removals

CGI Library Mostly Removed

Most of the CGI library has been removed, keeping only escape/unescape methods. If you need full CGI functionality, add the cgi gem to your Gemfile.

SortedSet No Longer Autoloaded

SortedSet is no longer available by default when requiring set.

# This no longer works in Ruby 3.5
require 'set'
sorted = SortedSet.new([3, 1, 2])

# Install the sorted_set gem instead
# gem 'sorted_set'
require 'sorted_set'
sorted = SortedSet.new([3, 1, 2])

Developer Action Required: Add gem 'sorted_set' to your Gemfile if you use SortedSet.

Testing Your Application

Since this is a preview release, now is the perfect time to test your applications for compatibility. You can install Ruby 3.5.0-preview1 and run your test suite to identify any issues before the final release.

Ruby 3.5 continues the tradition of improving developer experience with better concurrency primitives like Ractor::Port, performance optimizations, and cleaner language semantics, while maintaining strong backwards compatibility for most applications.

References

Prateek Choudhary

Technology Leader