gistfile1.rb

module Kernel
  def maybe(*path)
    return path.inject(self) do |obj, method|
      return nil if obj.nil?
      if method.respond_to? :keys
        obj.send(method.first[0], *method.first[1])
      else
        obj.respond_to?(:keys) ? obj[method] : obj.send(method)
      end
    end
  end
end


class Cart
  attr_reader :order
  def initialize(order = nil)
    @order = order
  end
end

class Order
  def initialize(lines = [])
    @lines = lines
  end

  def size()
    @lines.size
  end

  def line(index)
    @lines[index]
  end
end

class OrderLine
  attr_reader :product, :qty

  def initialize(product, qty=1)
    @product = product
    @qty = qty
  end
end

class Product
  attr_reader :name, :details
  def initialize(name, details = {})
    @name = name
    @details = details
  end
end


# no objects in call path are nil
cart = Cart.new(Order.new([ OrderLine.new(Product.new("Laptop"), 2), OrderLine.new(Product.new("Desktop"), 3) ]))
puts cart.maybe(:order, :size) # => 2
puts cart.maybe(:order, {:line => [1]}, :product, :name) # => Desktop

# the order is nil
emptyCart = Cart.new
puts emptyCart.maybe(:order, {:line => [1]}, :product, :name) # => nil

# the product on the first line item is nil
emptyLine = Cart.new Order.new([ OrderLine.new(nil) ])
puts emptyLine.maybe(:order, {:line => [0]}, :product, :name) # => nil

# retrieve hash values as well
line = OrderLine.new(Product.new("Keyboard", {:qwerty => true, :keys => 101}), 2)
puts line.maybe(:product, :details, :keys) # => 101