Remove Argument-Order Dependencies

I’m now working my way through the third chapter of Practical Object-Oriented Design in Ruby where we are learning about managing dependendies between objects.

Distracted by a shiny new operator

The first thing that I want to mention is the use of the ||= operator. I had never seen the “or equals” operator before and so I was distracted for awhile from this chapter until I read enough about it’s meaning to figure out what it does.

Using a hash as a paremeter

This chapter talk about several different ways to reduce your dependency on other objects, but the one about using a hash to pass in parameters really tickled my fancy. Here is an example class that I made up that passes in a hash of arguments.

class Foo
  attr_reader :apple, :orange, :taco, :juice

  def initialize(args)
    @apple  = args[:apple]
    @orange = args[:orange]
    @taco   = args[:taco]
    @juice  = args[:juice]
  end
  ...
end

Foo.new(
  :apple  => 3,
  :orange => 7,
  :taco   => Taco.new(14, 2),
  :juice  => 19).food_calculate

The benefits of using a hash are:

1. It removes every dependency on argument order
2. Adds verbosity
3. The key names in the hash tell us what we are passing in.

I really like point #3 because without the hash our code will be confusing and we won’t know what the numbers mean when we create a new Foo object like this:

Foo.new(3, 7, Taco.new(14, 2), 19).food_calculate

This section of the chapter really stood out to me because I really could have used this today at work to make it much more clear about what I was passing into one of my classes.