DRY Ruby Initialization with Hash Argument

Question

I find myself using hash arguments to constructors quite a bit, especially when writing DSLs for configuration or other bits of API that the end user will be exposed to. Wha

Answer 1

There are some useful things in Ruby for doing this kind of thing. The OpenStruct class will make the values of a has passed to its initialize method available as attributes on the class.

require 'ostruct'

class InheritanceExample < OpenStruct
end

example1 = InheritanceExample.new(:some => 'thing', :foo => 'bar')

puts example1.some  # => thing
puts example1.foo   # => bar

The docs are here: http://www.ruby-doc.org/stdlib-1.9.3/libdoc/ostruct/rdoc/OpenStruct.html

What if you don't want to inherit from OpenStruct (or can't, because you're already inheriting from something else)? You could delegate all method calls to an OpenStruct instance with Forwardable.

require 'forwardable'
require 'ostruct'

class DelegationExample
  extend Forwardable

  def initialize(options = {})
    @options = OpenStruct.new(options)
    self.class.instance_eval do
      def_delegators :@options, *options.keys
    end
  end
end

example2 = DelegationExample.new(:some => 'thing', :foo => 'bar')

puts example2.some  # => thing
puts example2.foo   # => bar

Docs for Forwardable are here: http://www.ruby-doc.org/stdlib-1.9.3/libdoc/forwardable/rdoc/Forwardable.html