RubyConf 2016 - Composition by James Dabbs

ruby-conf-composition.md

RubyConf 2016 - Composition by James Dabbs

• https://youtu.be/zwo7ZTHS8Wg

Category Theory

• study of composition
• a collection of objects
• functions between those objects
• the means to compose functions
• etc

Object Composition

• a object holding a reference to one or more other objects that is collaborates with to fulfill its responsibilities.
• has-a relationship (as opposed to inheritance's is-a)
• composition over inheritance
• f . g = f(g(x))

Guidelines for functional Ruby

• Objects should have a defined collection of fields. An object's state should be expressible entirely in terms of those fields.
• Fields should be set at initialization and then frozen. "Update" are performed by creating a new object.
• Objects should respond to call to perform their (primary) responsibility.

Advantages of using composition

our objects:

• have a clearly defined responsibility
• have a predictable interface
• are immutable
• have injectable dependencies
• are easy to configure and re-configure
• are easy to test
• are easy to mock in tests

componse method for callables

• https://youtu.be/zwo7ZTHS8Wg?t=2089
• Function composition >> Ruby

def call(sms)
  compose(
    :parse_message,
    :build_order,
    :validate_order,
    :record,
    :send_response
  ).call(sms)
end

def compose(*methods)
  ->(val) do
    result = val
    methods.each do |name|
      result = method(name).call(result)
    end
    result
  end
end