wrong number of arguments error while building a chainable ruby api

Question

In my gem I have a class called Client that I want to operate like this:

client = Client.new
client.content_type('pages').content_type

That means I want to set a property and then expect to immediately get it back in the same chain. This is what I have so far:

class Client
  attr_reader :content_type

  def initialize(options = {})
    @options = options
  end

  def content_type
    @content_type
  end

  def content_type(type_id)
    @content_type = type_id
    self
  end
end

Now when I try to run client.content_type('pages').content_type I get:

wrong number of arguments (given 0, expected 1) (ArgumentError)
    from chaining.rb:16:in `<main>'

What am I doing wrong? How do I write this correctly?

Answer 1

The names of your methods are conflicting. The second method is overriding the first. Either use different names or consolidate to do both like:

class Client
  attr_reader :content_type

  def initialize(options = {})
    @options = options
  end

  def content_type(type_id = nil)
    if type_id
      @content_type = type_id
      self
    else
      @content_type
    end
  end
end

Btw, this code stinks because the returned values for this are of different type depending on how it's called. You shouldn't do it unless you have a good reason to.