OpenStruct vs Struct vs Hash performance

open_struct_struct_hash.rb

require 'benchmark'
require 'ostruct'

REP = 1000000

User = Struct.new(:name, :age)

USER = "User".freeze
AGE = 21
HASH = {:name => USER, :age => AGE}.freeze

Benchmark.bm 20 do |x|
  x.report 'OpenStruct slow' do
    REP.times do |index|
       OpenStruct.new(:name => "User", :age => 21)
    end
  end

  x.report 'OpenStruct fast' do
    REP.times do |index|
       OpenStruct.new(HASH)
    end
  end

  x.report 'Struct slow' do
    REP.times do |index|
       User.new("User", 21)
    end
  end

  x.report 'Struct fast' do
    REP.times do |index|
       User.new(USER, AGE)
    end
  end

  x.report 'Hash slow' do
    REP.times do |index|
      {:name => 'User', :age => 21}
    end
  end

  x.report 'Hash fast' do
    REP.times do |index|
      {:name => USER, :age => AGE}
    end
  end
end

output

                           user     system      total        real
OpenStruct slow        8.150000   0.000000   8.150000 (  8.153797)
OpenStruct fast        7.980000   0.000000   7.980000 (  7.983929)
Struct slow            0.270000   0.000000   0.270000 (  0.268514)
Struct fast            0.200000   0.000000   0.200000 (  0.196950)
Hash slow              0.580000   0.000000   0.580000 (  0.584160)
Hash fast              0.460000   0.000000   0.460000 (  0.458502)

I changed the code to use benchmark-ips so that it's easier to read. I've also moved around and order fast first before the slow one, then moved the hashes to the top to make it the reference point.

Here's the code:

require 'benchmark/ips'
require 'ostruct'

User = Struct.new(:name, :age)

USER = "User".freeze
AGE = 21
HASH = {:name => USER, :age => AGE}.freeze

Benchmark.ips do |x|
  x.report('Hash fast') do
    {:name => USER, :age => AGE}
  end

  x.report('Hash slow') do
    {:name => 'User', :age => 21}
  end

  x.report('OpenStruct fast') do
    OpenStruct.new(HASH)
  end

  x.report('OpenStruct slow') do
    OpenStruct.new(:name => "User", :age => 21)
  end

  x.report('Struct fast') do
    User.new(USER, AGE)
  end

  x.report('Struct slow') do
    User.new("User", 21)
  end

  x.compare!(order: :baseline)
end

Here's the result for Ruby 3.4.1 on arm64 Macbook M4 Max (plugged):

ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [arm64-darwin24]
Warming up --------------------------------------
           Hash fast     2.128M i/100ms
           Hash slow     1.705M i/100ms
     OpenStruct fast    27.331k i/100ms
     OpenStruct slow    26.523k i/100ms
         Struct fast     1.237M i/100ms
         Struct slow     1.032M i/100ms
Calculating -------------------------------------
           Hash fast     21.367M (± 0.9%) i/s   (46.80 ns/i) -    108.524M in   5.079385s
           Hash slow     17.100M (± 1.3%) i/s   (58.48 ns/i) -     86.976M in   5.087229s
     OpenStruct fast    274.690k (± 1.1%) i/s    (3.64 μs/i) -      1.394M in   5.074963s
     OpenStruct slow    267.433k (± 0.7%) i/s    (3.74 μs/i) -      1.353M in   5.058272s
         Struct fast     12.257M (± 1.6%) i/s   (81.58 ns/i) -     61.867M in   5.048580s
         Struct slow     10.328M (± 1.3%) i/s   (96.83 ns/i) -     52.629M in   5.096724s

Comparison:
           Hash fast: 21367245.1 i/s
           Hash slow: 17100063.3 i/s - 1.25x  slower
         Struct fast: 12257262.0 i/s - 1.74x  slower
         Struct slow: 10327899.6 i/s - 2.07x  slower
     OpenStruct fast:   274690.4 i/s - 77.79x  slower
     OpenStruct slow:   267432.6 i/s - 79.90x  slower