Boolean method parameter assignment in Ruby

At first: prevent using boolean parameters in method definitions.
But let's assume you have to call a method that expects a boolean parameter like:

class Human
  def go backward=false
    puts "#{self.class} is going " + 
      (backward ? "backward" : "forward")
  end
end

A human can go forward and backward.
We want a human to go backward. If you would code it this way:

human = Human.new
# human goes backward
human.go true

please go on reading, because there is something to improve. At first the output is as expected:

Human is going backward

The code works but you have to agree, that "human.go true" is not readable (that's why there is a line of documentation). But we can improve the readability:

human = Human.new
human.go :backward

also results in:

Human is going backward

In Ruby a Symbol and all objects except instances of Nil and False class are true. Besides using an expressive Symbol can save the line of documentation, because the code documents itself. Awesome! Going forward could be default or explicit:

human = Human.new
human.go # default forward
human.go not(:backward) # explicit

The "not" before the Symbol inverts the assigned parameter. You also could use a bang ("human.go !:backward"). The result:

Human is going forward
Human is going forward

Though I'd prefer having a well designed API method ;-)

Supported by Ruby 1.9.3