Accessing instance variable in rails and ruby

Question

I am new to ruby and rails and sometimes I still get confused between these two. I have tried to call an instance variable by adding a name of the instance variable after an object(john.name), and I hope that the result would be John. Unfortunately NoMethodError appears. So I searched for an answer and found out that you can use instance_variable_get method to do this. However, I believe that it is possible to do this in RAILS when you want to access the instance variable of an object in VIEWS.

class Person
    def initialize(name)
        @name = name
    end
end
john = Person.new("John")
puts john.instance_variable_get(:@name)
=> John
puts john.name
=> NoMethodError

You can't access instance variable directly. Variables are generally part of something, confined within a method or class, say. But to get its value, you have it set it to a method or use attr_accessor. Below two answers show you how. — arjun
– arjun, Commented Mar 12, 2017 at 13:07
Ruby is simple. All an object exposes are methods. You can't access instance variables from outside directly. — Aetherus
– Aetherus, Commented Mar 12, 2017 at 13:20
@arjun, You don't need an accessor: class C; def initialize; @x = 1; end; end; C.new.instance_variable_get(:@x) #=> 1. — Cary Swoveland
– Cary Swoveland, Commented Mar 12, 2017 at 20:37
Assuming that the variable appears once in the code. But generally variables are modified many times and I believe, that the proper way is to define it in a class method and call that instead. — arjun
– arjun, Commented Mar 12, 2017 at 20:41

Rajdeep Singh · Accepted Answer · 2017-03-12 12:52:29Z

2

Use attr_reader to read the value of an instance variable

class Person
  attr_reader :name

  def initialize(name)
    @name = name
  end
end

john = Person.new("John")
john.name #=> "John"

attr_reader adds a getter method to the class, in this case

def name
  @name
end

Hope that helps!

answered Mar 12, 2017 at 12:52

Rajdeep Singh

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Comments

Gaurav Soni · Accepted Answer · 2017-03-12 12:55:09Z

1

You need to define the method to access your instance variable.

class Person
  def initialize(name)
    @name = name
  end

  def name
    @name
  end
end

Or you can simply add attr_accessor which will set getter and setter methods

class Person
  attr_accessor :name

  def initialize(name)
    @name = name
  end
end

edited Mar 12, 2017 at 12:55

answered Mar 12, 2017 at 12:47

Gaurav Soni

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