Ruby Class Relationships: How do I use methods and objects from another class?

Question

Thanks for viewing my question! :)

I'm fairly new to programming in Ruby, and I'm having trouble understanding how to implement classes in my code, and having them inherit methods and variable from each other.

I have a class LightBulb, which looks like this:

class LightBulb
  def initialize( watts, on )
    @watts = watts
    @on = on
  end

  # accessor methods
  def watts
    @watts
  end

  def on
    @on
  end

  # other methods
  def turnon
    @on = true
  end

  def turnoff
    @on = false
  end

  def to_s
    "#{@watts}-#{@on}"
  end
end

and the driver program that works with the class:

# a lit, 30-watt bulb

b = LightBulb.new( 30, false )
b.turnon( )
Bulb    

# a 50-watt bulb

fiftyWatt = LightBulb.new( 50, false )
fiftyWatt.turnoff( )

...and I'm trying to create a class Lamp that has-a LightBulb and uses it at various times. I know that on the inheritance tree diagram, they are supposed to be next to each other (i.e. LightBulb--Lamp, instead of LightBulb<--Lamp), so I don't know if I should be using the < inheritance operator. Here's the basic structure I need for the Lamp class:

Lamp ( string make, string model, double cost, int watts )
-- accessors
string make( ) 
string model( ) 
-- methods
void turnon( ) # turn on the bulb
void turnoff( ) # turn off the bulb
--class members
string make
string model
double cost
LightBulb bulb

How would I be able to use the turnon() and turnoff() methods from the LightBulb class, as well as the bulb object, in the Lamp class?

Here's what I have for Lamp so far, but I'm sure most of it is incorrect:

class Lamp
    attr_accessor :watts
    def initialize(make, model, cost, watts)
        @make = make
        @model = model
        @cost = cost
        @watts = LightBulb.new(:watts)
    end

    def make
        @make
    end

    def model
        @model
    end

    def cost
        @cost
    end
end

Answer 1

You definitely don't need inheritance here. You are composing these objects, a Lamp has a LightBulb. You're close, and all you really need to do is call the methods on LightBulb that you're missing:

class Lamp

  def initialize(make, model, cost, watts)
    @make = make
    @model = model
    @cost = cost
    @bulb = LightBulb.new(watts, false)
  end

  # ... 

  def turnon
    @bulb.turnon
  end

  def turnoff
    @bulb.turnoff
  end

end

So I changed @watts to @bulb, and dropped the :watts symbol, as you really need to pass the value of watts that was passed in. If you're interested, here is some more information on symbols.