Accessing variables using overloading brackets [] in Ruby

Question

Hi i want to do the following. I simply want to overload the [] method in order to access the instance variables... I know, it doesn't make great sense at all, but i want to do this for some strange reason :P

It will be something like this...

class Wata

    attr_accessor :nombre, :edad

    def initialize(n,e)
        @nombre = n
        @edad   = e
    end

    def [](iv)
        self.iv
    end

end

juan = Wata.new('juan',123)

puts juan['nombre']

But this throw the following error:

overload.rb:11:in `[]': undefined method 'iv' for # (NoMethodError)

How can i do that?

EDIT

I have found also this solution:

def [](iv)
    eval("self."+iv)
end

Chuck · Accepted Answer · 2009-12-14 20:18:13Z

8

Variables and messages live in a different namespace. In order to send the variable as a message, you'd need to define it as either:

def [](iv)
    send iv
end

(if you want to get it through an accessor)

or

def [](iv)
    instance_variable_get "@#{iv}"
end

(if you want to access the ivar directly)

answered Dec 14, 2009 at 20:18

Chuck

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2 Comments

flyer88 Over a year ago

Excellent Chuck! I didn't know anything about sending a variable... It also works with instance_variable_get Thanks..

khelll Over a year ago

send works with methods only, attr_accessor adds both setter and getter methods for you, so send basically is calling the getter.

khelll · Accepted Answer · 2009-12-14 20:16:23Z

4

try instance_variable_get instead:

 def [](iv)
     instance_variable_get("@#{iv}")
 end

answered Dec 14, 2009 at 20:16

khelll

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