An example of creating a custom accessor type to parse inputs.

date_accessor.rb

#!/usr/bin/ruby

require 'date'

class Resource
  def initialize(hash = {})
    hash.each { |k, v| send("#{k}=", v) if respond_to?("#{k}=") }
  end
  
  class << self
    def date_writer(*args)
      args.each do |attr|
        define_method("#{attr.to_s}=".to_sym) do |date|
          date = date.is_a?(String) ? DateTime.parse(date) : date
          instance_variable_set("@#{attr}", date)
        end
      end
    end
  
    def date_accessor(*args)
      attr_reader *args
      date_writer *args
    end
  end
end

class Post < Resource
  date_accessor :published_at
end

post = Post.new(published_at: '2015-07-16T08:04:31Z')
puts post.published_at