June 3, 2025

If you’re like me and enjoy digging into Ruby performance, you’ll appreciate the latest improvements in Ruby 3.5 — especially when it comes to how fast objects get allocated.

Thanks to optimizations in Class#new, Ruby 3.5 dramatically improves allocation performance for both positional and keyword arguments. And with YJIT enabled, the numbers are even more impressive.

Here’s a simplified example from the benchmarks:

require "benchmark"

class Person
  def initialize(name:, age:, city:)
    @name = name
    @age = age
    @city = city
  end
end

Benchmark.bm do |x|
  x.report("allocating with keywords") do
    1_000_000.times do
      Person.new(name: "Jane", age: 32, city: "Rosario")
    end
  end
end

In Ruby 3.5, this runs up to 6.5x faster than in Ruby 3.4 when YJIT is enabled. That’s a major win for apps that create lots of objects — think Rails controllers, background jobs, serializers, etc.

It’s always fascinating to see low-level improvements like this pay off at the app level without needing to change any code.

Ruby 3.5 Brings Serious Speed to Object Allocation

Big thanks to @aaron Patterson and the Ruby team for the continued work on making Ruby not only expressive, but also fast.

Full write-up here: railsatscale.com/2025-05-21-fast-allocations-in-ruby-3-5

ruby #ruby3_5 #performance #yjit #rails #backend #programming #devlife