A little lesson in ruby methods

gistfile1.md

Methods in ruby have a special feature if the last attribute is a hash

def dashed_keys(h1, h2)
  "h1(#{ h1.keys.join("-") }) h2(#{ h2.keys.join("-") })"
end

> dashed_keys({:a => 1, :b => 2}, {:m => 13, :n => 14})
=> "h1(a-b) h2(m-n)"

You don't even need the curly brackets for the last one. You just need it for the first one so ruby knows where one hash ends and the other starts.

> dashed_keys({:a => 1, :b => 2}, :m => 13, :n => 14)
=> "h1(a-b) h2(m-n)"

Lets look at another function

def dashed_keys(h)
  h.keys.join("-")
end

If you try to call this method by itself, it will fail

> dashed_keys
ArgumentError: wrong number of arguments (0 for 1)

You can get around this with a default value

def dashed_keys(h = {})
  h.keys.join("-")
end

> dashed_keys(h)
=> ""

This is why you'll often see in Rails methods an optional hash at the end. For example see text_field.

text_field(object_name, method, options = {})

It lets you do things like:

text_field :message, :title, :id => "msg_title", :class => "red"