class Polygon
attr_accessor :sides
@sides = 10
end
When I try to access
puts Polygon.new.sides # => nil
I get nil. How to access sides? What is wrong here?
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3Hmm, downvotes. Well, +1 from me. JVK gave an example, showed what he tried, and the desired output is obvious.DigitalRoss– DigitalRoss2012-10-30 18:37:21 +00:00Commented Oct 30, 2012 at 18:37
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1Don't understand the down votes, its a good questionManjunath Manoharan– Manjunath Manoharan2012-10-30 18:42:15 +00:00Commented Oct 30, 2012 at 18:42
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@DigitalRoss I am a newbie and learning Ruby for few days now. And it seems few people think stackoverflow is not for newbie to ask question.JVK– JVK2012-10-30 18:42:26 +00:00Commented Oct 30, 2012 at 18:42
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Thank you all to answer this foobar question for a ruby newbie :)JVK– JVK2012-10-30 18:43:46 +00:00Commented Oct 30, 2012 at 18:43
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It was a perfectly good question, keep asking. :-)DigitalRoss– DigitalRoss2012-10-30 18:47:12 +00:00Commented Oct 30, 2012 at 18:47
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4 Answers
Since ruby class definitions are just executable code, when you say @sides = 10 in the context of a class definition, you're defining that on Polygon (not instances of Polygon):
class Polygon
attr_accessor :sides
@sides = 10
end
Polygon.instance_variables
# => [:@sides]
You probably want to set the number of sides on the instances of Polygon, from the initializer:
class Polygon
attr_accessor :sides
def initialize(sides)
@sides = sides
end
end
Polygon.new(10).sides
# => 10
Comments
This exact question (even uses the same example code you have), is answered on railstips.org.
Comments
The attr_accessor, in short defines two methods.
def sides
end
def sides=
end
To get the value of the sides which have mentioned here, you need to init them in
def initialize
@sides = 10
end
answered Oct 30, 2012 at 18:25
Manjunath Manoharan
4,6276 gold badges30 silver badges43 bronze badges
Comments
You need:
def initialize
@sides = 10
end
By assigning to @sides at the class level, you created a class instance variable rather than an instance variable of the object you created with #new.
In this case, you have an attribute of a given Polygon, but if it was actually an attribute of the class (like author or copyright or something) then you could reference it via the @whatever syntax if you were in a class method, created with def self.something ... end.
