more informative Hash#fetch

class Hash

  # A better implementation of Hash#fetch, which will return a default
  # parameter passed in, the result of the passed in block
  # OR throw IndexError if the key is not in the hash
  # fetch! is a version of this function that returns the name of the key that was
  # not found in the hash.
  # For a good detail of the Hash#fetch method see:
  # <http://avdi.org/devblog/2009/03/16/go-fetch/>
  def fetch!(key, default_value=nil, &block)
    begin
      if block_given?
        self.fetch(key, &block)
      else
        if default_value
          self.fetch(key, default_value)
        else
          self.fetch(key)
        end
      end
    rescue IndexError => e
      raise IndexError, "key '#{key}' not found"
    end
  end

end

def tests
  t = {"a" => 1}
  p t.fetch!("b", "something")
  
  t.fetch!("b") {puts "no worries, mate!"}
  t.fetch!("b")
end

tests