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Create "immutable" objects. No setters, just getters!

Create "immutable" objects. No setters, just getters!


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This gem allows you to define "immutable" objects, and your objects will have only getters and no setters. So, if you change [1] [2] some object attribute, you will have a new object instance. That is, you transform the object instead of modifying it.

Table of contents

Installation

Add this line to your application's Gemfile and bundle install:

gem 'u-attributes'

Compatibility

u-attributes branch ruby activemodel
2.4.0 main >= 2.2.0 >= 3.2, < 6.1
1.2.0 v1.x >= 2.2.0 >= 3.2, < 6.1

Note: The activemodel is an optional dependency, this module can be enabled to validate the attributes.

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Usage

How to define attributes?

By default, you must define the class constructor.

class Person
  include Micro::Attributes

  attribute :age
  attribute :name

  def initialize(name: 'John Doe', age:)
    @name, @age = name, age
  end
end

person = Person.new(age: 21)

person.age  # 21
person.name # John Doe

# By design the attributes are always exposed as reader methods (getters).
# If you try to call a setter you will see a NoMethodError.
#
# person.name = 'Rodrigo'
# NoMethodError (undefined method `name=' for #<Person:0x0000... @name='John Doe', @age=21>)

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Micro::Attributes#attributes=

This is a protected method to make easier the assignment in a constructor. e.g.

class Person
  include Micro::Attributes

  attribute :age
  attribute :name, default: 'John Doe'

  def initialize(options)
    self.attributes = options
  end
end

person = Person.new(age: 20)

person.age  # 20
person.name # John Doe

How to extract attributes from an object or hash?

You can extract attributes using the extract_attributes_from method, it will try to fetch attributes from the object using either the object[attribute_key] accessor or the reader method object.attribute_key.

class Person
  include Micro::Attributes

  attribute :age
  attribute :name, default: 'John Doe'

  def initialize(user:)
    self.attributes = extract_attributes_from(user)
  end
end

# extracting from an object

class User
  attr_accessor :age, :name
end

user = User.new
user.age = 20

person = Person.new(user: user)

person.age  # 20
person.name # John Doe

# extracting from a hash

another_person = Person.new(user: { age: 55, name: 'Julia Not Roberts' })

another_person.age  # 55
another_person.name # Julia Not Roberts

Is it possible to define an attribute as required?

You only need to use the required: true option.

But to this work, you need to assign the attributes using the #attributes= method or the extensions: initialize, activemodel_validations.

class Person
  include Micro::Attributes

  attribute :age
  attribute :name, required: true

  def initialize(attributes)
    self.attributes = attributes
  end
end

Person.new(age: 32) # ArgumentError (missing keyword: :name)

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Micro::Attributes#attribute

Use this method with a valid attribute name to get its value.

person = Person.new(age: 20)

person.attribute('age') # 20
person.attribute(:name) # John Doe
person.attribute('foo') # nil

If you pass a block, it will be executed only if the attribute was valid.

person.attribute(:name) { |value| puts value } # John Doe
person.attribute('age') { |value| puts value } # 20
person.attribute('foo') { |value| puts value } # !! Nothing happened, because of the attribute doesn't exist.

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Micro::Attributes#attribute!

Works like the #attribute method, but it will raise an exception when the attribute doesn't exist.

person.attribute!('foo')                   # NameError (undefined attribute `foo)

person.attribute!('foo') { |value| value } # NameError (undefined attribute `foo)

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How to define multiple attributes?

Use .attributes with a list of attribute names.

class Person
  include Micro::Attributes

  attributes :age, :name

  def initialize(options)
    self.attributes = options
  end
end

person = Person.new(age: 32)

person.name # nil
person.age  # 32

Note: This method can't define default values. To do this, use the #attribute() method.

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Micro::Attributes.with(:initialize)

Use Micro::Attributes.with(:initialize) to define a constructor to assign the attributes. e.g.

class Person
  include Micro::Attributes.with(:initialize)

  attribute :age, required: true
  attribute :name, default: 'John Doe'
end

person = Person.new(age: 18)

person.age  # 18
person.name # John Doe

This extension enables two methods for your objects. The #with_attribute() and #with_attributes().

#with_attribute()

another_person = person.with_attribute(:age, 21)

another_person.age            # 21
another_person.name           # John Doe
another_person.equal?(person) # false

#with_attributes()

Use it to assign multiple attributes

other_person = person.with_attributes(name: 'Serradura', age: 32)

other_person.age            # 32
other_person.name           # Serradura
other_person.equal?(person) # false

If you pass a value different of a Hash, a Kind::Error will be raised.

Person.new(1) # Kind::Error (1 expected to be a kind of Hash)

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Defining default values to the attributes

To do this, you only need make use of the default: keyword. e.g.

class Person
  include Micro::Attributes.with(:initialize)

  attribute :age
  attribute :name, default: 'John Doe'
end

There are two different strategies to define default values.

  1. Pass a regular object, like in the previous example.
  2. Pass a proc/lambda, and if it has an argument you will receive the attribute value to do something before assign it.
class Person
  include Micro::Attributes.with(:initialize)

  attribute :age, default: -> age { age&.to_i }
  attribute :name, default: -> name { String(name || 'John Doe').strip }
end

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The strict initializer

Use .with(initialize: :strict) to forbids an instantiation without all the attribute keywords.

In other words, it is equivalent to you define all the attributes using the required: true option.

class StrictPerson
  include Micro::Attributes.with(initialize: :strict)

  attribute :age
  attribute :name, default: 'John Doe'
end

StrictPerson.new({}) # ArgumentError (missing keyword: :age)

An attribute with a default value can be omitted.

person_without_age = StrictPerson.new(age: nil)

person_without_age.age  # nil
person_without_age.name # 'John Doe'

Note: Except for this validation the .with(initialize: :strict) method will works in the same ways of .with(:initialize).

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Is it possible to inherit the attributes?

Yes. e.g.

class Person
  include Micro::Attributes.with(:initialize)

  attribute :age
  attribute :name, default: 'John Doe'
end

class Subclass < Person # Will preserve the parent class attributes
  attribute :foo
end

instance = Subclass.new({})

instance.name              # John Doe
instance.respond_to?(:age) # true
instance.respond_to?(:foo) # true

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.attribute!()

This method allows us to redefine the attributes default data that was defined in the parent class. e.g.

class AnotherSubclass < Person
  attribute! :name, default: 'Alfa'
end

alfa_person = AnotherSubclass.new({})

alfa_person.name # 'Alfa'
alfa_person.age  # nil

class SubSubclass < Subclass
  attribute! :age, default: 0
  attribute! :name, default: 'Beta'
end

beta_person = SubSubclass.new({})

beta_person.name # 'Beta'
beta_person.age  # 0

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How to query the attributes?

All of the methods that will be explained can be used with any of the built-in extensions.

PS: We will use the class below for all of the next examples.

class Person
  include Micro::Attributes

  attribute :age
  attribute :first_name, default: 'John'
  attribute :last_name, default: 'Doe'

  def initialize(options)
    self.attributes = options
  end

  def name
    "#{first_name} #{last_name}"
  end
end

.attributes

Listing all the class attributes.

Person.attributes # ["age", "first_name", "last_name"]

.attribute?()

Checking the existence of some attribute.

Person.attribute?(:first_name)  # true
Person.attribute?('first_name') # true

Person.attribute?('foo') # false
Person.attribute?(:foo)  # false

#attribute?()

Checking the existence of some attribute in an instance.

person = Person.new(age: 20)

person.attribute?(:name)  # true
person.attribute?('name') # true

person.attribute?('foo') # false
person.attribute?(:foo)  # false

#attributes()

Fetching all the attributes with their values.

person1 = Person.new(age: 20)
person1.attributes # {"age"=>20, "first_name"=>"John", "last_name"=>"Doe"}

person2 = Person.new(first_name: 'Rodrigo', last_name: 'Rodrigues')
person2.attributes # {"age"=>nil, "first_name"=>"Rodrigo", "last_name"=>"Rodrigues"}

#attributes(keys_as:)

Use the keys_as: option with Symbol/:symbol or String/:string to transform the attributes hash keys.

person1 = Person.new(age: 20)
person2 = Person.new(first_name: 'Rodrigo', last_name: 'Rodrigues')

person1.attributes(keys_as: Symbol) # {:age=>20, :first_name=>"John", :last_name=>"Doe"}
person2.attributes(keys_as: String) # {"age"=>nil, "first_name"=>"Rodrigo", "last_name"=>"Rodrigues"}

person1.attributes(keys_as: :symbol) # {:age=>20, :first_name=>"John", :last_name=>"Doe"}
person2.attributes(keys_as: :string) # {"age"=>nil, "first_name"=>"Rodrigo", "last_name"=>"Rodrigues"}

#attributes(*names)

Slices the attributes to include only the given keys (in their types).

person = Person.new(age: 20)

person.attributes(:age)               # {:age => 20}
person.attributes(:age, :first_name)  # {:age => 20, :first_name => "John"}
person.attributes('age', 'last_name') # {"age" => 20, "last_name" => "Doe"}

person.attributes(:age, 'last_name') # {:age => 20, "last_name" => "Doe"}

# You could also use the keys_as: option to ensure the same type for all of the hash keys.

person.attributes(:age, 'last_name', keys_as: Symbol) # {:age=>20, :last_name=>"Doe"}

#attributes([names])

As the previous example, this methods accepts a list of keys to slice the attributes.

person = Person.new(age: 20)

person.attributes([:age])               # {:age => 20}
person.attributes([:age, :first_name])  # {:age => 20, :first_name => "John"}
person.attributes(['age', 'last_name']) # {"age" => 20, "last_name" => "Doe"}

person.attributes([:age, 'last_name']) # {:age => 20, "last_name" => "Doe"}

# You could also use the keys_as: option to ensure the same type for all of the hash keys.

person.attributes([:age, 'last_name'], keys_as: Symbol) # {:age=>20, :last_name=>"Doe"}

#attributes(with:, without:)

Use the with: option to include any method value of the instance inside of the hash, and, you can use the without: option to exclude one or more attribute keys from the final hash.

person = Person.new(age: 20)

person.attributes(without: :age)               # {"first_name"=>"John", "last_name"=>"Doe"}
person.attributes(without: [:age, :last_name]) # {"first_name"=>"John"}

person.attributes(with: [:name], without: [:first_name, :last_name]) # {"age"=>20, "name"=>"John Doe"}

# To achieves the same output of the previous example, use the attribute names to slice only them.

person.attributes(:age, with: [:name]) # {:age=>20, "name"=>"John Doe"}

# You could also use the keys_as: option to ensure the same type for all of the hash keys.

person.attributes(:age, with: [:name], keys_as: Symbol) # {:age=>20, :name=>"John Doe"}

#defined_attributes

Listing all the available attributes.

person = Person.new(age: 20)

person.defined_attributes # ["age", "first_name", "last_name"]

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Built-in extensions

You can use the method Micro::Attributes.with() to combine and require only the features that better fit your needs.

But, if you desire except one or more features, use the Micro::Attributes.without() method.

Picking specific features

Micro::Attributes.with

Micro::Attributes.with(:initialize)

Micro::Attributes.with(:initialize, :keys_as_symbol)

Micro::Attributes.with(:keys_as_symbol, initialize: :strict)

Micro::Attributes.with(:diff, :initialize)

Micro::Attributes.with(:diff, initialize: :strict)

Micro::Attributes.with(:diff, :keys_as_symbol, initialize: :strict)

Micro::Attributes.with(:activemodel_validations)

Micro::Attributes.with(:activemodel_validations, :diff)

Micro::Attributes.with(:activemodel_validations, :diff, initialize: :strict)

Micro::Attributes.with(:activemodel_validations, :diff, :keys_as_symbol, initialize: :strict)

The method Micro::Attributes.with() will raise an exception if no arguments/features were declared.

class Job
  include Micro::Attributes.with() # ArgumentError (Invalid feature name! Available options: :activemodel_validations, :diff, :initialize, :keys_as_symbol)
end

Micro::Attributes.without

Picking except one or more features

Micro::Attributes.without(:diff) # will load :activemodel_validations, :keys_as_symbol and initialize: :strict

Micro::Attributes.without(initialize: :strict) # will load :activemodel_validations, :diff and :keys_as_symbol

Picking all the features

Micro::Attributes.with_all_features

# This method returns the same of:

Micro::Attributes.with(:activemodel_validations, :diff, :keys_as_symbol, initialize: :strict)

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Extensions

ActiveModel::Validation extension

If your application uses ActiveModel as a dependency (like a regular Rails app). You will be enabled to use the activemodel_validations extension.

class Job
  include Micro::Attributes.with(:activemodel_validations)

  attribute :id
  attribute :state, default: 'sleeping'

  validates! :id, :state, presence: true
end

Job.new({}) # ActiveModel::StrictValidationFailed (Id can't be blank)

job = Job.new(id: 1)

job.id    # 1
job.state # 'sleeping'

.attribute() options

You can use the validate or validates options to define your attributes. e.g.

class Job
  include Micro::Attributes.with(:activemodel_validations)

  attribute :id, validates: { presence: true }
  attribute :state, validate: :must_be_a_filled_string

  def must_be_a_filled_string
    return if state.is_a?(String) && state.present?

    errors.add(:state, 'must be a filled string')
  end
end

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Diff extension

Provides a way to track changes in your object attributes.

require 'securerandom'

class Job
  include Micro::Attributes.with(:initialize, :diff)

  attribute :id
  attribute :state, default: 'sleeping'
end

job = Job.new(id: SecureRandom.uuid())

job.id    # A random UUID generated from SecureRandom.uuid(). e.g: 'e68bcc74-b91c-45c2-a904-12f1298cc60e'
job.state # 'sleeping'

job_running = job.with_attribute(:state, 'running')

job_running.state # 'running'

job_changes = job.diff_attributes(job_running)

#-----------------------------#
# #present?, #blank?, #empty? #
#-----------------------------#

job_changes.present? # true
job_changes.blank?   # false
job_changes.empty?   # false

#-----------#
# #changed? #
#-----------#
job_changes.changed? # true

job_changes.changed?(:id)    # false

job_changes.changed?(:state) # true
job_changes.changed?(:state, from: 'sleeping', to: 'running') # true

#----------------#
# #differences() #
#----------------#
job_changes.differences # {'state'=> {'from' => 'sleeping', 'to' => 'running'}}

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Initialize extension

  1. Creates a constructor to assign the attributes.
  2. Add methods to build new instances when some data was assigned.
class Job
  include Micro::Attributes.with(:initialize)

  attributes :id, :state
end

job_null = Job.new({})

job.id    # nil
job.state # nil

job = Job.new(id: 1, state: 'sleeping')

job.id    # 1
job.state # 'sleeping'

##############################################
# Assigning new values to get a new instance #
##############################################

#-------------------#
# #with_attribute() #
#-------------------#

new_job = job.with_attribute(:state, 'running')

new_job.id          # 1
new_job.state       # running
new_job.equal?(job) # false

#--------------------#
# #with_attributes() #
#--------------------#
#
# Use it to assign multiple attributes

other_job = job.with_attributes(id: 2, state: 'killed')

other_job.id          # 2
other_job.state       # killed
other_job.equal?(job) # false

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Strict mode

  1. Creates a constructor to assign the attributes.
  2. Adds methods to build new instances when some data was assigned.
  3. Forbids missing keywords.
class Job
  include Micro::Attributes.with(initialize: :strict)

  attributes :id, :state
end
#-----------------------------------------------------------------------#
# The strict initialize mode will require all the keys when initialize. #
#-----------------------------------------------------------------------#

Job.new({})

# The code above will raise:
# ArgumentError (missing keywords: :id, :state)

#---------------------------#
# Samples passing some data #
#---------------------------#

job_null = Job.new(id: nil, state: nil)

job.id    # nil
job.state # nil

job = Job.new(id: 1, state: 'sleeping')

job.id    # 1
job.state # 'sleeping'

Note: This extension works like the initialize extension. So, look at its section to understand all of the other features.

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Keys as symbol extension

Disables the indifferent access requiring the declaration/usage of the attributes as symbols.

The advantage of this extension over the default behavior is because it avoids an unnecessary allocation in memory of strings. All the keys are transformed into strings in the indifferent access mode, but, with this extension, this typecasting will be avoided. So, it has a better performance and reduces the usage of memory/Garbage collector, but gives for you the responsibility to always use symbols to set/access the attributes.

class Job
  include Micro::Attributes.with(:initialize, :keys_as_symbol)

  attribute :id
  attribute :state, default: 'sleeping'
end

job = Job.new(id: 1)

job.attributes # {:id => 1, :state => "sleeping"}

job.attribute?(:id) # true
job.attribute?('id') # false

job.attribute(:id) # 1
job.attribute('id') # nil

job.attribute!(:id) # 1
job.attribute!('id') # NameError (undefined attribute `id)

As you could see in the previous example only symbols will work to do something with the attributes.

This extension also changes the diff extension making everything (arguments, outputs) working only with symbols.

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Development

After checking out the repo, run bin/setup to install dependencies. Then, run rake test 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.

Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/serradura/u-attributes. 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.

License

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

Code of Conduct

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

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