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rubyattributesinitialization
mottalrd
mottalrd

Reputation: 4490

Ruby fields initialization

In this tiny class when the @sides=10 statement is executed?
How this statement is related to the initialize method? 

class Poligon
    attr_accessor :sides
    @sides=10
end

I am mostly used to Java where it is common to have inline initialization for the attributes. I am now trying to understand the complete initialization procedure for Ruby but I was not able to find it.

Upvotes: 0

Views: 3312

Answers (3)

toro2k
toro2k

Reputation: 19228

Short answers:

  • The statemen @sides = 0 (which actually is an expression) is exectuted when the class expression in evaluated.

  • It is not related at all with the initialize method.

As you write it, the @sides variable is a class instance variable, i.e. an instance variable of the Poligon object (remember that in Ruby classes are objects of class Class). You must initialize instance variables inside a method definitions (perhaps inside the initialize method). Consider this example:

class Poligon
  @class_sides = 'class instance variable'
  def initialize
    @instance_sides = 'instance variable'
  end
end

Poligon.instance_variables
# => [:@class_sides]

Poligon.instance_variable_get(:@class_sides)
# => "class instance variable" 

Poligon.new.instance_variables
# => [:@instance_sides] 

Poligon.new.instance_variable_get(:@instance_sides)
# => "instance variable"

For more information about class instance variable and how they relate to class variables you can read this article by Martin Fowler.

Upvotes: 3

anthv123
anthv123

Reputation: 523

The initialize method is the constructor for the class. If you want, you can initialize your instance variables in the contructor:

class Poligon
    attr_accessor :sides

    def initialize(num_sides)
      @sides = num_sides
    end
end

But since @sides is declared as an attr_accessor, you can set/get it directly:

p = Poligon.new
p.sides = 10

Upvotes: 3

Arup Rakshit
Arup Rakshit

Reputation: 118271

You need to put this @sides=10 inside a method,with your current class definition.

class Poligon
    attr_accessor :sides
    def line
     @sides=10
    end
end

p = Poligon.new
p.line
puts p.sides
# >> 10

Upvotes: 3

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