Ruby 可以在 class 內定義 exception method，這樣就可以 raise 這個 class

不囉唆，上 code

Raising Non-Exceptions

If we provide an exception method, any object can be raised as an exception.

Imagine you have a class called HTMLSafeString which contains a string of text. You might want to make it possible to pass one of these “safe” strings to raise just like a normal string. To do this we simply add an exception method that creates a new RuntimeError.

class HTMLSafeString
  def initialize(value)
    @value = value
  end
 
  def exception
    RuntimeError.new(@value)
  end
end

raise HTMLSafeString.new("helloworld")”


Excerpt From: Starr Horne. “Mastering Ruby Exceptions.” iBooks.