test_shape_search.rb

class A
  def foo
    @foo
  end

  def initialize
    @foo = 123
    40.times do
      instance_variable_set(:"@var_#{_1}", _1)
    end
  end
end

A.new # warm A's size pool

obj1 = A.new
obj2 = A.new.freeze

N = ENV.fetch("N", 10_000_000).to_i
N.times do
  obj1.foo
  obj2.foo
end

test_shape_search_deep.rb

class A
  def foo
    @foo
  end

  def initialize(bar = false)
    @bar = 123 if bar
    @foo = 123
    40.times do
      instance_variable_set(:"@var_#{_1}", _1)
    end
  end
end

A.new # warm A's size pool

obj1 = A.new
obj2 = A.new(true)

N = ENV.fetch("N", 10_000_000).to_i
N.times do
  obj1.foo
  obj2.foo
end