Accord - object interfaces and adaptation for Ruby

Accord is a gem providing basic object interface and adaptation support for Ruby. An interface represents a protocol or contract (an API), and this gem allows you to label your objects/classes/modules as being compliant with a given API by declaring them as implementing/providing interfaces. Thus, one would call this an implementation of ‘Design by Contract <en.wikipedia.org/wiki/Design_by_contract>`_ in Ruby.

Object adaptation is also supported. Given an object which claims to provide some API, and in a specific point of the code another API is needed, Accord will allow adapting from the object API to the desired one (provided that an adapter which can adapt the APIs is known by Accord).

This gem was largely inspired by the Python package “zope.interface“, maintained by the ‘Zope Toolkit Project <docs.zope.org/zopetoolkit/>`_. “zope.interface“ source `can be found here <github.com/zopefoundation/zope.interface>`_.

Disclaimer: this is not used in any real world project yet. The API is still changing (and will, while this gem is not in the 1.0 version). Not ready for prime time.

Basic usage

---

Declare some interfaces

Labelled = Accord::Interface(:Labelled) do

responds_to :label

end PersonAPI = Accord::Interface(:PersonAPI)

Implement them

class Person

attr_reader :name
def initialize(name)
  @name = name
end

end

class PersonLabel

def initialize(person)
  @person = person
end
def label
  @person.name
end

end

Declare that your classes are implementations of the interfaces

Accord::Declarations.implements(Person, PersonAPI) Accord::Declarations.implements(PersonLabel, Labelled)

Tell Accord that people can have labels (that is, they can be adapted to

‘Labelled`)

Accord.default_adapter_registry.register(, Labelled) do |person|

PersonLabel.new(person)

end

Now, in a piece of code which needs a label

def show(object)

Labelled.adapt!(object).label

end

When a person is given to ‘#show`, its name will be used to provide a label

person = Person.new(‘John’) show(person) #=> ‘John’

By registering more adapters, ‘#show` can be reused to show the labels of other types of objects, without changing its source. `#show` doesn’t rely on receiving a person, but depends only on an interface. Also, everything could have been added in the application after the ‘Person` class (as if that class were legacy code), without modifying its source. Or `Person` could be a class in a third party library.

License

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This gem is MIT-licensed. See LICENSE.txt in the root of this repository.