🧱 μ-struct

Create powered Ruby structs.

Table of contents: <!-- omit in toc -->

• Introduction
  • Motivation
• Installation
• Usage
  • Micro::Struct.new
  • optional: option
  • required: option
  • Defining custom methods/behavior
  • Micro::Struct.with
  • Micro::Struct[]
  • :to_ary
  • :to_hash
  • :to_proc
  • :readonly
  • :instance_copy
  • :exposed_features
  • Micro::Struct.instance or Micro::Struct.with(...).instance
  • Micro::Struct.immutable
  • Micro::Struct.readonly
  • TL;DR
• FAQ
  • How to override the Struct .new method?
  • Can I override the Struct initializer?
• Development
• Contributing
• License
• Code of Conduct
• Contact
• Acknowledgments

Introduction

Ruby Struct is a versatile data structure because it can behave like an Array, Hash, and ordinary object:

Person = Struct.new(:first_name, :last_name)

person = Person.new('Rodrigo', 'Serradura')
# #<struct Person first_name="Rodrigo", last_name="Serradura">

# -- Ordinary object behavior --

person.first_name # "Rodrigo"
person.last_name  # "Serradura"

person.first_name = 'John' # "John"
person.last_name = 'Doe'   # "Doe"

person
# #<struct Person first_name="John", last_name="Doe">

# -- Hash behavior --

person[:first_name] # "Doe"
person['last_name'] # "John"

person[:first_name] = 'Rodrigo'   # "Rodrigo"
person['last_name'] = 'Serradura' # "Serradura"

person
# #<struct Person first_name="Rodrigo", last_name="Serradura">


# Transforming a Struct into a Hash
person.to_h
# {:first_name=>"Rodrigo", :last_name=>"Serradura"}

# -- Array behavior --

person[0] # "Rodrigo"
person[1] # "Serradura"

person[0] = 'John' # "John"
person[1] = 'Doe'  # "Doe"

person
# #<struct Person first_name="John", last_name="Doe">

# Transforming a Struct into an Array
person.to_a
# ["John", "Doe"]

Because of these characteristics, structs could be excellent candidates to create different kinds of POROs (Plain Old Ruby Objects). However, it is very common to see developers avoiding its usage because of some of its behaviors, like setters or the constructor's positional arguments. The addition of keywords arguments on its constructor (available on Ruby >= 2.5) improved the experience to instantiate Struct objects but it doesn't require all the arguments. Some developers can still feel uncomfortable with that and they might avoid its usage.

Look at the example showing the Struct's keyword_init: option creating a constructor with optional keyword arguments:

Person = Struct.new(:first_name, :last_name, keyword_init: true)

Person.superclass # Struct

Person.new
# #<struct Person first_name=nil, last_name=nil>

# Because of this, you will only see an exception
# if you pass one or more invalid keywords.

Person.new(foo: 1, bar: 2)
# ArgumentError (unknown keywords: foo, bar)

Motivation

So, given this introduction, the idea of this project is to provide a way of creating Ruby Structs with some powerful features. Let's see how the Micro::Struct.new() works.

require 'u-struct'

Person = Micro::Struct.new(:first_name, :last_name)

Person.superclass
# Struct

Person.new
# ArgumentError (missing keywords: :first_name, :last_name)

As you can see, the struct instantiation raised an error because all of the keywords arguments are required.

If you need one or many optional arguments, you can use the optional: option to define them:

Person = Micro::Struct.new(:first_name, optional: :last_name)

Person.new
# ArgumentError (missing keyword: :first_name)

Person.new(first_name: 'Rodrigo')
# #<struct Person first_name="Rodrigo", last_name=nil>

If you want a Struct only with optional members (or attributes), as the keyword_init: option does, you can declare all attributes within the optional: option:

Person = Micro::Struct.new(optional: [:first_name, :last_name])

Person.new
# #<struct Person first_name=nil, last_name=nil>

You can also use the required: option to define required attributes.

Person = Micro::Struct.new(
  required: [:first_name, :last_name],
  optional: [:age]
)

So, what did you think? If you liked it, continue the reading to understand what this gem can do for you.

Installation

Add this line to your application's Gemfile:

gem 'u-struct'

And then execute:

$ bundle install

Or install it yourself as:

$ gem install u-struct

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Usage

Micro::Struct.new

Like Struct.new, you will use Micro::Struct.new to create your Struct classes.

The key difference is: the Struct created from Micro::Struct will use keyword arguments in their constructors.

Person = Struct.new(:name)          # Person
Persona = Micro::Struct.new(:name)  # Persona

Person.ancestors  # [Person, Struct, Enumerable, Object, Kernel, BasicObject]
Persona.ancestors # [Person, Struct, Enumerable, Object, Kernel, BasicObject]

Person.new('Rodrigo')        # #<struct Person name="Rodrigo">
Persona.new(name: 'Rodrigo') # #<struct Person name="Rodrigo">

Person.new  # #<struct Person name=nil>

Persona.new # ArgumentError (missing keyword: :name)

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optional: option

If you need optional attributes, you can use this to define them.

Person = Micro::Struct.new(:name, optional: :age)

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

Person.new(name: 'John')
# #<struct Person name="John", age=nil>

Use an array to define multiple optional attributes.

Person = Micro::Struct.new(:name, optional: [:age, :nickname])

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

Person.new(name: 'John')
# #<struct Person name="John", age=nil, nickname=nil>

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required: option

It is an alternative way to define required attributes. Use a symbol to define one or an array to define multiple attributes.

Person = Micro::Struct.new(
  required: [:first_name, :last_name],
  optional: [:age]
)

Person.new
# ArgumentError (missing keywords: :first_name, :last_name)

Person.new first_name: 'John', last_name: 'Doe'
# #<struct Person first_name="John", last_name="Doe", age=nil>

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Defining custom methods/behavior

The Micro::Struct.new accepts a block as a regular Struct, and you can use it to define some custom behavior/methods.

Person = Micro::Struct.new(:first_name, :last_name, optional: :age) do
  def name
    "#{first_name} #{last_name}"
  end
end

person = Person.new(first_name: 'Rodrigo', last_name: 'Serradura')
# #<struct Person first_name="Rodrigo", last_name="Serradura", age=nil>

person.first_name # "Rodrigo"
person.last_name  # "Serradura"
person.name       # "Rodrigo Serradura"

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Micro::Struct.with

This method can do two things: first, it can create Struct factories; second, it sets some special behavior to their structs.

These are all of the available features which you can use (pick one, many, or all of them):

• :to_ary
• :to_hash
• :to_proc
• :readonly
• :instance_copy
• :exposed_features

Look at an example of defining a Struct factory that can create "immutable" structs by picking the :readonly, :instance_copy features.

ReadonlyStruct = Micro::Struct.with(:readonly, :instance_copy)

# Use the factory to create structs with the same characteristics:

Person = ReadonlyStruct.new(:first_name, :last_name)

person = Person.new(first_name: 'Rodrigo', last_name: 'Rodrigues')
# #<struct Person first_name="Rodrigo", last_name="Rodrigues">

# The `:readonly` sets all the Struct writers as private.

person.last_name = ''
# NoMethodError (private method `last_name=' called for #<struct Person ...>)

person[:last_name] = ''
# NoMethodError (private method `[]=' called for #<struct Person ...>)

# The `:instance_copy` defines a `#with` instance method,
# which allows you to create a new instance from the current struct state.

new_person = person.with(last_name: 'Serradura')
# #<struct Person first_name="Rodrigo", last_name="Serradura">

new_person == person
# false

new_person.class == person.class
# true

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Micro::Struct[]

The [] brackets method is as an alias of Micro::Struct.with. e.g.

Micro::Struct[:readonly, :to_hash] # is the same as Micro::Struct.with(:readonly, :to_hash)

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:to_ary

Defines a #to_ary method which will invoke the struct #to_a method. If you override the #to_a method you will also affect it.

The #to_ary makes Ruby know how to deconstruct an object like an array.

Person = Micro::Struct.with(:to_ary).new(:first_name, :last_name)

person = Person.new(first_name: 'Rodrigo', last_name: 'Serradura')

first_name, last_name = person

p first_name # "Rodrigo"
p last_name  # "Serradura"

*first_and_last_name = person

p first_and_last_name # ["Rodrigo", "Serradura"]

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:to_hash

Defines a #to_hash method which will invoke the struct #to_h method. If you override the #to_h method you will also affect it.

The #to_hash makes Ruby know how to deconstruct an object like a hash.

Person = Micro::Struct.with(:to_hash).new(:first_name, :last_name)

person = Person.new(first_name: 'Rodrigo', last_name: 'Serradura')

def greet(first_name:, last_name:)
  puts "Hi #{first_name} #{last_name}!"
end

greet(**person)
# Hi Rodrigo Serradura!

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:to_proc

The #to_proc tells Ruby how to invoke it as a block replacement (by using &).

The lambda returned from the #to_proc will require a hash as its argument.

Person = Micro::Struct.with(:to_proc).new(:first_name, :last_name)

[
  {first_name: 'John', last_name: 'Doe'},
  {first_name: 'Mary', last_name: 'Doe'}
].map(&Person)
# [
#  #<struct Person::Struct first_name="John", last_name="Doe">,
#  #<struct Person::Struct first_name="Mary", last_name="Doe">
# ]

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:readonly

This feature sets the Struct members' writers as private.

Person = Micro::Struct.with(:readonly).new(:first_name, :last_name)

person = Person.new(first_name: 'Rodrigo', last_name: 'Rodrigues')
# #<struct Person first_name="Rodrigo", last_name="Rodrigues">

person.last_name = ''
# NoMethodError (private method `last_name=' called for #<struct Person ...>)

person[:last_name] = ''
# NoMethodError (private method `[]=' called for #<struct Person ...>)

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:instance_copy

Creates the #with method, which will instantiate a struct of the same kind and reuse its current state.

Person = Micro::Struct.with(:instance_copy).new(:first_name, :last_name)

person = Person.new(first_name: 'Rodrigo', last_name: 'Serradura')
# => #<struct Person::Struct first_name="Rodrigo", last_name="Serradura">

person.first_name = 'John'
# => "John"

person.inspect
# => #<struct Person::Struct first_name="John", last_name="Serradura">

new_person = person.with(last_name: 'Doe')
# => #<struct Person::Struct first_name="John", last_name="Doe">

person === new_person     # => false
person.equal?(new_person) # => false

person.last_name     # => "Serradura"
new_person.last_name # => "Doe"

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:exposed_features

This feature exposes the struct's configured features. Via the methods: .features and .__features__.

Person = Micro::Struct.with(:exposed_features, :readonly, :to_proc).new(:name)

Person.features
# => #<struct Micro::Struct::Features::Exposed
#      names=[:readonly, :to_proc],
#      options={:to_ary=>false, :to_hash=>false, :to_proc=>true, :readonly=>true, :instance_copy=>false}>

Person.__features__.equal?(Person.features) # `.__features__` is an alias of `.features` method

Person.features.names   # => [:readonly, :to_proc]
Person.features.options # => {:to_ary=>false, :to_hash=>false, :to_proc=>true, :readonly=>true, :instance_copy=>false}

Person.features.option?(:to_proc)  # => true
Person.features.option?(:readonly) # => true

Person.features.options?(:to_proc)  # => true
Person.features.options?(:readonly) # => true

Person.features.options?(:to_proc, :readonly) # => true
Person.features.options?(:to_ary, :readonly)  # => false

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Micro::Struct.instance or Micro::Struct.with(...).instance

Creates a struct instance from a given hash. This could be useful to create constants or a singleton value.

person1 = Micro::Struct.instance(first_name: 'Rodrigo', last_name: 'Serradura')
# => #<struct  first_name="Rodrigo", last_name="Serradura">

person1.first_name = 'John'

person1.first_name # => "John"

You can also use the instance method after defining some struct feature (Micro::Struct.with).

person2 = Micro::Struct.with(:readonly).instance(first_name: 'Rodrigo', last_name: 'Serradura')
# => #<struct  first_name="Rodrigo", last_name="Serradura">

person2.first_name = 'John'
# NoMethodError (private method `first_name=' called for #<struct first_name="Rodrigo", last_name="Serradura">)

And if you need some custom behavior, use a block to define them.

person3 = Micro::Struct.instance(first_name: 'Rodrigo', last_name: 'Serradura') do
  def name
    "#{first_name} #{last_name}"
  end
end

person4 = Micro::Struct.with(:readonly).instance(first_name: 'Rodrigo', last_name: 'Serradura') do
  def name
    "#{first_name} #{last_name}"
  end
end

person3.name # => "Rodrigo Serradura"
person4.name # => "Rodrigo Serradura"

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Micro::Struct.immutable

This method is as a shortcut to Micro::Struct.with(:readonly, :instance_copy). As it is quite common to see the usage of these two features, I decided to create this method to improve the DX.

Additional info:

1. It accepts the with: option, which can be used to define additional features.
2. The .instance method can be called after its usage.

Usage examples:

Micro::Struct.immutable.new(:name)

Micro::Struct.immutable.new(:name) do
  def hi(other_name)
    "Hi, #{other_name}! My name is #{name}"
  end
end

Micro::Struct.immutable(with: :to_hash).new(:name)

Micro::Struct.immutable(with: [:to_hash, :to_proc]).new(:name)

Micro::Struct.immutable.instance(name: 'Rodrigo')

Micro::Struct.immutable(with: [:to_hash]).instance(name: 'Serradura')

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Micro::Struct.readonly

This method is as a shortcut to Micro::Struct.with(:readonly).

Additional info:

1. It accepts the with: option, which can be used to define additional features.
2. The .instance method can be called after its usage.

Usage examples:

Micro::Struct.readonly.new(:name)

Micro::Struct.readonly.new(:name) do
  def hi(other_name)
    "Hi, #{other_name}! My name is #{name}"
  end
end

Micro::Struct.readonly(with: :to_hash).new(:name)

Micro::Struct.readonly(with: [:to_hash, :to_proc]).new(:name)

Micro::Struct.readonly.instance(name: 'Rodrigo')

Micro::Struct.readonly(with: [:to_hash]).instance(name: 'Serradura')

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TL;DR

Like in a regular Struct, you can define one or many attributes but all of them will be required by default.

Micro::Struct.new(:first_name, :last_name, ...)

Use the optional: argument if you want some optional attributes.

Micro::Struct.new(:first_name, :last_name, optional: :gender)

# Using `optional:` to define all attributes are optional.

Micro::Struct.new(optional: [:first_name, :last_name])

Use the required: argument to define required attributes.

Micro::Struct.new(
  required: [:first_name, :last_name],
  optional: [:gender, :age]
)

You can also pass a block to define custom methods.

Micro::Struct.new(:name) {}

Available features (use one, many, or all) to create Structs with a special behavior:

Micro::Struct.with(:to_ary)
Micro::Struct.with(:to_ary, :to_hash)
Micro::Struct.with(:to_ary, :to_hash, :to_proc)
Micro::Struct.with(:to_ary, :to_hash, :to_proc, :readonly)
Micro::Struct.with(:to_ary, :to_hash, :to_proc, :readonly, :instance_copy)
Micro::Struct.with(:to_ary, :to_hash, :to_proc, :readonly, :instance_copy, :exposed_features)

All of the possible combinations to create a Ruby Struct using Micro::Struct:

Micro::Struct.new(*required)
Micro::Struct.new(*required) {}

Micro::Struct.new(optional: *)
Micro::Struct.new(optional: *) {}

Micro::Struct.new(required: *)
Micro::Struct.new(required: *) {}

Micro::Struct.new(*required, optional: *)
Micro::Struct.new(*required, optional: *) {}

Micro::Struct.new(required: *, optional: *)
Micro::Struct.new(required: *, optional: *) {}

Any options above can be used by the .new() method of the struct creator returned by the .with() method.

Micro::Struct.with(*features).new(...) {}

Use Micro::Struct.instance() or Micro::Struct.with(...).instance() to create a struct instance from a given hash.

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FAQ

How to override the Struct .new method?

The .new is an alias for the .__new__ method, so you can use .__new__ when overriding it.

module RGB
  Number = ->(value) do
    return value if value.is_a?(::Integer) && value >= 0 && value <= 255

    raise TypeError, "#{value} must be an Integer(>= 0 and <= 255)"
  end

  Color = Micro::Struct.new(:red, :green, :blue) do
    def self.new(r, g, b)
      __new__(
        red: Number[r],
        green: Number[g],
        blue: Number[b],
      )
    end

    def to_hex
      "##{red}#{green}#{blue}"
    end
  end
end

rgb_color = RGB::Color.new(1, 5, 255)
# => #<struct RGB::Color::Struct red=#<struct RGB::Number value=1>, green=#<struct RGB::Number value=5>, blue=#<struct RGB::Number value=255>>

rgb_color.to_hex
# => "#0105ff"

RGB::Color.new(-1, 5, 255)
# => TypeError: -1 must be an Integer(>= 0 and <= 255)

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Can I override the Struct initializer?

Yes, you can, but the initializer must handle the arguments as positional ones.

RGBColor = Micro::Struct.with(:readonly, :to_ary).new(:red, :green, :blue) do
  Number = ->(value) do
    return value if value.is_a?(::Integer) && value >= 0 && value <= 255

    raise TypeError, "#{value} must be an Integer(>= 0 and <= 255)"
  end

  def initialize(r, g, b)
    super(Number[r], Number[g], Number[b])
  end

  def to_hex
    '#%02x%02x%02x' % self
  end
end

rgb_color = RGBColor.new(red: 1, green: 1, blue: 255)
# #<struct RGBColor red=1, green=1, blue=255>

r, g, b = rgb_color

[r,g,b]
# [1, 1, 255]

rgb_color.to_hex
# "#0101ff"

RGBColor.new(red: 1, green: -1, blue: 255)
# TypeError (-1 must be an Integer(>= 0 and <= 255))

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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.

Additional tools:

• Sorbet (type checker): bundle exec srb tc (requires Ruby >= 2.7).
• Rubocop (linter and code formatter): bundle rubocop (requires Ruby >= 2.5).

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 the created tag, and push the .gem file to rubygems.org.

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Contributing

Bug reports and pull requests are welcome on GitHub at https://github.com/serradura/u-struct. This project is intended to be a safe, welcoming space for collaboration, and contributors are expected to adhere to the code of conduct.

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License

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

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Code of Conduct

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

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Contact

Rodrigo Serradura - Twitter | LinkedIn.

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Acknowledgments

• @vitoravelino thanks for talking about some gem's ideas and reviewing the documentation.