Defining a fast immutable Struct

immutable_struct.rb

# Defining a fast immutable struct while
# keeping Struct value object behaviour

class ImmutableStruct < Struct
  undef []=, send

  def self.inherited(subclass)
    subclass.instance_methods.grep(/\w=/) do |setter|
      undef_method setter
    end
  end
end

# Make an immutable Struct by subclassing only
class MyImmutable < ImmutableStruct.new(:one, :two); end

o = MyImmutable.new(1,2)

p o.respond_to?('[]=')    # => false
p o.respond_to?('one=')   # => false
p o.respond_to?('two=')   # => false
p o.respond_to?('send')   # => false

# Bencharking against the Struct
require 'benchmark/ips'

RegularStruct = Struct.new(:flip, :flap)

Benchmark.ips do |x|
  x.report('Immutable Struct:') do
    MyImmutable.new(1,2)
  end

  x.report('Regular Struct:') do
    RegularStruct.new(1,2)
  end

  x.compare!
end

__END__
Calculating -------------------------------------
   Immutable Struct:   103.865k i/100ms
     Regular Struct:   102.135k i/100ms
-------------------------------------------------
   Immutable Struct:      3.168M (± 2.7%) i/s -     15.891M
     Regular Struct:      3.394M (± 2.0%) i/s -     17.057M

Comparison:
     Regular Struct::  3394240.6 i/s
   Immutable Struct::  3168228.5 i/s - 1.07x slower