InitCopy

🧬 Easily use the correct clone or dup method in initialize_copy.

If we only use either clone or dup or we use Marshal, then that does not produce the correct behavior according to the standard documentation. This is because clone should preserve the internal state (e.g., the frozen state and extended modules), while dup should not. For example:

module SecretExt
  def secret
    'password'
  end
end

# Init vars.
bob = 'Bob'
bob.extend(SecretExt)
bob.freeze

clone = bob.clone
dup   = bob.dup

# Check vars.
puts clone.frozen? #=> true
puts dup.frozen?   #=> false

puts clone.secret  #=> password
puts dup.secret    #=> NoMethodError

To solve this issue in the past, we had to define both initialize_clone & initialize_dup and maintain two copies of all our deep-copy code. That sucks. 😞

🚀 Instead, InitCopy was created:

1. Install the gem init_copy (on RubyGems.org).
2. Include InitCopy::Able in your class/module.
3. Override the init_copy(original) method.
4. Use ic_copy(var), instead of clone/dup.

Example usage:

require 'init_copy'

class JangoFett
  include InitCopy::Able

  attr_reader :gear,:bounties,:order66

  def initialize
    super

    @gear = ['blaster','jetpack']
    @bounties = ['Padmé','Vosa']

    @order66 = Class.new do
      undef_method :clone
      undef_method :dup
    end.new
  end

  protected

  def init_copy(_orig)
    super

    @gear = ic_copy(@gear)
    @bounties = ic_copy(@bounties)

    @order66 = ic_copy?(@order66) # Safe copy if no dup/clone.
  end
end

# Init vars.
jango = JangoFett.new
jango.bounties.freeze

boba1 = jango.clone
boba2 = jango.dup

jango.gear << 'vibroblade'
boba1.gear << 'implant'

# Check vars.
puts jango.gear.inspect     #=> ["blaster", "jetpack", "vibroblade"]

puts boba1.gear.inspect     #=> ["blaster", "jetpack", "implant"]
puts boba2.gear.inspect     #=> ["blaster", "jetpack"]

puts boba1.bounties.inspect #=> ["Padmé", "Vosa"]
puts boba2.bounties.inspect #=> ["Padmé", "Vosa"]

puts boba1.bounties.frozen? #=> true  (clone)
puts boba2.bounties.frozen? #=> false (dup)

// Contents

• Setup
• Hacking
• License

// Setup

Pick your poison...

With the RubyGems CLI package manager:

gem install init_copy

In your Gemspec:

spec.add_dependency 'init_copy', '~> X.X'

In your Gemfile:

# Pick your poison...
gem 'init_copy', '~> X.X'
gem 'init_copy', git: 'https://github.com/esotericpig/init_copy.git', branch: 'main'

From source:

git clone --depth 1 'https://github.com/esotericpig/init_copy.git'
cd init_copy
bundle install
bundle exec rake install:local

// Hacking

git clone 'https://github.com/esotericpig/init_copy.git'
cd init_copy
bundle install
bundle exec rake -T

Testing:

bundle exec rake test

Generating doc:

bundle exec rake clobber_doc doc

Installing:

bundle exec rake install:local

// License

Copyright (c) 2020-2025 Bradley Whited
MIT License