CODEWITHSUNDEEP
rubylearn-ruby-the-hard-way
Suresh
Suresh

Reputation: 39

Not displaying it's corresponding values with it's key for Hash

Ok i am not here to ask for an answer. But to be honest i am not really good in class variable. So i would appreciate you can guide me along with this piece of code.

I have read on class variable at those docs. I some what kind of understand it. But it comes to applying it for my own use. I would get confused.

class Square

   @@sqArray = {}

    #attr_accessor :length

   def initialize
      if defined?(@@length)
        randno = "%s" % [rand(20)]
        @@length = randno.to_i
        @@sqArray = @@length

    else 
        randno = "%s" % [rand(20)]
        @@length = randno.to_i
        @@sqArray = @@length
    end
   end

   def Area
         @@area = @@length * @@length
         return @@area
         @@sqArray[@@length.to_sym] = @@area
         puts @@sqArray
   end  
   end

        s1 = Square.new
        puts s1.Area

Let me explain this piece of code. Basically every time i create a Square object it would go to initialize method. A random number will be generated and pass it to @@length, and @@length will be assigned to hash @@sqArray as it's key. But now the problem is when i create a new object s1. When i want to display the Area i want to test out to print the hash @@sqArray with it's length as it's key and area as it's value. But now the problem is only returning it's area only. e.g 114 only. suppose to be e.g [ 24 => 114]

Upvotes: 0

Views: 33

Answers (1)

Tom Lord
Tom Lord

Reputation: 28305

When defining the object's property (i.e. it's length), the correct approach is to use an instance variable, not a class variable. This is because (in your particular example), length is an attribute of a specific square and not something that applies to all squares. Your code should look something like this:

class Square
  def initialize(length = rand(20))
    @length = length
  end

  def area
    @length * @length
  end
end

s1 = Square.new
puts s1.area

Now, I am a little unclear what exactly you aim to achieve by use of that class variable @@sqArray - but for example, you could use this store a list of all defined Squares:

class Square
  @@squares_list = []
  def self.all_known
    @@squares_list
  end

  def initialize(length = rand(20))
    @length = length
    @@squares_list << self
  end

  def area
    @length * @length
  end
end

This would allow you to write code like:

s1 = Square.new     #=> #<Square:0x0000000132dbc8 @length=9>
s2 = Square.new(20) #=> #<Square:0x000000012a1038 @length=20>
s1.area             #=> 81
s2.area             #=> 400
Square.all_known    #=> [#<Square:0x0000000132dbc8 @length=9>, #<Square:0x000000012a1038 @length=20>]

Class variables have some odd behaviour and limited use cases however; I would generally advise that you avoid them when starting out learning Ruby. Have a read through a ruby style guide to see some common conventions regarding best practice - including variable/method naming (use snake_case not camelCase or PascalCase), whitespace, etc.

Upvotes: 1

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