ruby inheritance

Question

How to implement inheritance in ruby for the following?

class Land
  attr_accessor :name, :area
  def initialize(name, area)
    @name = name
    @area = area
  end
end

class Forest < Land
  attr_accessor :rain_level
  attr_reader :name

  def name=(_name)
    begin
      raise "could not set name"
    rescue  Exception => e
            puts e.message  
        end
  end

  def initialize(land, rain_level)
    @name = land.name
    @rain_level = rain_level
  end
end

l = Land.new("land", 2300)
f = Forest.new(l, 400)
puts f.name # => "land"

suppose when i change name for land l, then it should change for sub class also

l.name ="new land"
puts f.name # => "land"

what expected is puts f.name # => "new land"

Jonas Elfström · Accepted Answer · 2012-11-20 09:50:21Z

2

It seems to me that this is not actually inheritance in the OO sense. If you change Forest so that it holds a reference to the Land then you will get the behavior you wanted.

class Forest
  attr_accessor :rain_level

  def name
    @land.name
  end

  def initialize(land, rain_level)
    @land = land
    @rain_level = rain_level
  end
end

answered Nov 20, 2012 at 9:50

Jonas Elfström

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4 Comments

Arivarasan L Over a year ago

yes, it can achieved without inheritance. How can approach it in inheritance way?. like father can set and get value and son only get the value

Jonas Elfström Over a year ago

Inheritance just doesn't work that way. If you shave the mustache of your father it doesn't mean that your upper lip will also be shaved.

Arivarasan L Over a year ago

i understand, i expect something like if my father changes his address then my address should change automatically. If my expectation is not a kind of inheritance then please ignore it.

Jonas Elfström Over a year ago

"For example, consider a class Person that contains a person's name, address, phone number, age, gender, and race. We can define a subclass of Person called Student that contains the person's grade point average and classes taken, and another subclass of Person called Employee that contains the person's job-title, employer, and salary." en.wikipedia.org/wiki/Inheritance_(computer_science)

Joshua · Accepted Answer · 2012-11-20 09:37:13Z

0

This is kind of an interesting thing you want to build.

Summarizing you want to have two objects that share a value but only one is allowed to edit the value, the other one is only allowed to read it.

I think the easiest way to implement this is in your case to implement a new getter in Forest which returns land.name. By writing l.name = 'meow' will f.name return moew too because it holds a reference to l.

Hope this helps.

answered Nov 20, 2012 at 9:37

Joshua

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