https://dev.to/edisonywh/a-tale-of-curiosity-at-work-work-doesn-t-have-to-be-boring-2122

benchmark_memoize_hash.rb

require 'objspace'

class Foo
  def self.memo_hash
    @_memo_hash ||= begin
      Hash.new(100)
    end
  end
end

class Bar
  def self.hash
    Hash.new(100)
  end
end

class Baz
  BAZ = Hash.new(100)
end

def object_count
  ObjectSpace.count_objects[:T_HASH]
end

puts "Init: #{object_count}"

Foo.memo_hash
puts "Foo init: #{object_count}"
100.times do
  Foo.memo_hash
end
puts "Foo final: #{object_count}"

Bar.hash
puts "Bar init: #{object_count}"
100.times do
  Bar.hash
end
puts "Bar final: #{object_count}"

Baz.hash
puts "Baz init: #{object_count}"
100.times do
  Baz.hash
end
puts "Baz final: #{object_count}"

# Result
# 
# > Init: 66
# > Foo init: 68
# > Foo final: 69
# > Bar init: 71
# > Bar final: 172
# > Baz init: 173
# > Baz final: 174
#
# As you can see, if I don't memoize it it creates 100 more objects in memory!