Evil::Struct

Nested structure with type constraints, based on the dry-initializer DSL.

Installation

Add this line to your application's Gemfile:

gem 'evil-struct'

And then execute:

$ bundle

Or install it yourself as:

$ gem install evil-struct

Synopsis

The structure is like dry-struct except for it controls optional attributes and default values aside of type constraints.

Its DSL is taken from dry-initializer. Its method attribute is just an alias for option.

require "evil-struct"
require "dry-types"

class Product < Evil::Struct
  attribute :title
  attribute :price,    Dry::Types["coercible.float"]
  attribute :quantity, Dry::Types["coercible.int"], default: proc { 0 }

  # shared options
  attributes optional: true do
    attribute :subtitle
    attribute :description
  end
end

# Accepts both symbolic and string keys.
# Class methods `[]`, `call`, and `load` are just aliases for `new`
product = Product[title: "apple", "price" => "10.9", description: "a fruit"]

# Attributes are available via methods or `[]`
product.title       # => "apple"
product[:price]     # => 10.9
product["quantity"] # => 0
product.description # => "a fruit"

# unassigned value differs from `nil`
product.subtitle    # => Dry::Initializer::UNDEFINED

# Raises in case a mandatory value not assigned
Product.new # BOOM! because neither title, nor price are assigned

# Hashifies all attributes except for undefined subtitle
# You can use `dump` as an alias for `to_h`
product.to_h
# => { title: "apple", price: 10.9, description: "a fruit", quantity: 0 }

# The structure is comparable to any object that responds to `#to_h`
product == { title: "apple", price: 10.9, description: "a fruit", quantity: 0 }
# => true

The structure is designed for immutability. That's why it doesn't contain writers (but you can define them by yourself via attr_writer).

Instead of mutating current instance, you can merge another hash to the object via merge or deep_merge.

new_product = product.merge(title: "orange")
new_product.class # => Product
new_product.to_h
# => { title: "orange", price: 10.9, description: "a fruit", quantity: 0 }

# you can merge any object that responds to `to_h` or `to_hash`
other = Product[title: "orange", price: 12]
new_product = product.merge(other)
new_product.to_h
# => { title: "orange", price: 12, description: "a fruit", quantity: 0 }

# merge_deeply (deep_merge) gracefully merge nested hashes or hashified objects
grape = Product.new title: "grape",
                    price: 30,
                    description: { country: "FR", year: 2016, sort: "Merlot" }

new_grape = grape.merge_deeply description: { year: 2017 }
new_grape.to_h
# => {
#      title: "grape",
#      price: 30,
#      description: { country: "FR", year: 2017, sort: "Merlot" }
#     }

Compatibility

Tested under rubies compatible to MRI 2.2+.

Contributing

Fork the project
Create your feature branch (git checkout -b my-new-feature)
Add tests for it
Commit your changes (git commit -am '[UPDATE] Add some feature')
Push to the branch (git push origin my-new-feature)
Create a new Pull Request

License

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

evil-struct