immutable_struct_ex is yet another immutable struct. What makes immutable_struct_ex different, is that it allows you to create immutable structs in one step by default. In other words, other immutable struct gems force you to first define the struct, then instantiate the struct object; or, define the struct and instantiate the struct object via chaining. For example:

# Two steps...
some_immutable_struct = SomeImmutableStruct.new(:first, :last, :phone)
some_immutable_struct.new(first: 'John', last: 'Doe', phone: '(201) 230-7281')

# Chaining...
some_immutable_struct = SomeImmutableStruct.new(:first, :last, :phone)
                          .new(first: 'John', last: 'Doe', phone: '(201) 230-7281')

immutable_struct_ex allows you to instantiate and initialize the object in one step:

immutable_struct_ex = ImmutableStructEx.new(first: 'John', last: 'Doe', phone: '(201) 230-7281')

immutable_struct_ex.first
#=> 'John'

immutable_struct_ex[:first]
#=> 'John'

immutable_struct_ex.last
#=> 'Doe'

immutable_struct_ex.phone
#=> '(201) 230-7281'

Like other immutable structs, immutable_struct_ex also removes methods that change the state of the object, making it immutable:

immutable_struct_ex.first = 'Joe'
#=> NoMethodError: undefined method `first='...

immutable_struct_ex[:first] = 'Joe'
#=> NoMethodError: undefined method `[]='...

Also, not unlike other immutable structs, immutable_struct_ex also allows you to pass a block:

# With a block
immutable_struct_ex = ImmutableStructEx.new(first: 'John', last: 'Doe', phone: '(201) 230-7281') do
  def john?
    first == 'John'
  end
end

immutable_struct_ex.john?
#=> true

Get creative. Below is an example of an immutable struct that provides redaction:

# Redactable, immutable struct
user = {
  username: 'jdoe',
  password: 'p@55w0rD',
  ssn: '123-70-9182'
}

immutable_struct_ex = ImmutableStructEx.new(**user) do
  REDACT = %i(password ssn).freeze

  def inspect
    to_s
  end

  def to_s
    super.to_s.tap do |string|
      REDACT.each do |redact|
        string.gsub!(/( #{Regexp.quote(redact.to_s)}=")(.*?)(")/, '\1[REDACTED]\3')
      end
    end
  end

  def to_h
    super.to_h.tap do |hash|
      REDACT.each { |redact| hash[redact] = '[REDACTED]' }
    end
  end
end

immutable_struct_ex.inspect
#=> "#<struct username=\"jdoe\", password=\"[REDACTED]\", ssn=\"[REDACTED]\">"

immutable_struct_ex.to_h
#=> {:username=>"jdoe", :password=>"[REDACTED]", :ssn=>"[REDACTED]"}

Add this line to your application's Gemfile:

gem 'immutable_struct_ex'

And then execute:

$ bundle

Or install it yourself as:

$ gem install immutable_struct_ex

After checking out the repo, run bin/setup to install dependencies. Then, run rake spec to run the tests. You can also run bin/console for an interactive prompt that will allow you to experiment.

To install this gem onto your local machine, run bundle exec rake install. To release a new version, update the version number in version.rb, and then run bundle exec rake release, which will create a git tag for the version, push git commits and tags, and push the .gem file to rubygems.org.

Bug reports and pull requests are welcome on GitHub at https://github.com/[USERNAME]/immutable_struct_ex. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the Contributor Covenant code of conduct.

The gem is available as open source under the terms of the MIT License.

Everyone interacting in the ImmutableStructEx project’s codebases, issue trackers, chat rooms and mailing lists is expected to follow the code of conduct.