Ruby Class vs Struct

Question

I have seen codebases using Structs to wrap around attributes and behavior inside a class. What is the difference between a Ruby Class and a Struct? And when should one be used

Answer 1

I'd like to to @sam_forgot suggested benchmark. The comparison is not very fair. Both class and struct, these days, support keyword arguments. Using keyword arguments on each has opposite effects, as you can see from my example struct's with keyword arguments performance is not that dramatically different from the class.

require 'benchmark'

REP=1000000

SUser = Struct.new(:name, :age)
SUserK = Struct.new(:name, :age, keyword_init: true)

DATA = { name: "Harry", age: 75 }
DATA2 = DATA.values

class CUser
  attr_accessor :name, :age
  def initialize(name, age)
    @name = name
    @age = age
  end
end

class CUserK
  attr_accessor :name, :age
  def initialize(name:, age:)
    @name = name
    @age = age
  end
end

Benchmark.bmbm do |x|
  x.report 'Struct create and access, without keyword arguments' do
    REP.times do
      user = SUser.new(DATA)
      "#{user.name} - #{user.age}"
    end
  end

  x.report 'Struct create and access, with keyword arguments' do
    REP.times do
      user = SUserK.new(**DATA)
      "#{user.name} - #{user.age}"
    end
  end

  x.report 'Class create and access, without keyword arguments' do
    REP.times do
      user = CUser.new(*DATA2)
      "#{user.name} - #{user.age}"
    end
  end 

  x.report 'Class create and access, with keyword arguments' do
    REP.times do
      user = CUserK.new(DATA)
      "#{user.name} - #{user.age}"
    end
  end
end

Rehearsal ---------------------------------------------------------------------------------------
Struct create and access, without keyword arguments   3.484609   0.011974   3.496583 (  3.564523)
Struct create and access, with keyword arguments      0.965959   0.005543   0.971502 (  1.007738)
Class create and access, without keyword arguments    0.624603   0.003999   0.628602 (  0.660931)
Class create and access, with keyword arguments       0.901494   0.004926   0.906420 (  0.952149)
------------------------------------------------------------------------------ total: 6.003107sec

                                                          user     system      total        real
Struct create and access, without keyword arguments   3.300488   0.010372   3.310860 (  3.339511)
Struct create and access, with keyword arguments      0.876742   0.004354   0.881096 (  0.903551)
Class create and access, without keyword arguments    0.553393   0.003962   0.557355 (  0.568985)
Class create and access, with keyword arguments       0.831672   0.004811   0.836483 (  0.850224)