Access instance variable from outside the class

Question

If an instance variable belongs to a class, can I access the instance variable (e.g. @hello) directly using the class instance?

class Hello   def method1     @hello = "pavan"   end end  h = Hello.new puts h.method1 

Answer 1

Yes, you can use instance_variable_get like this:

class Hello   def method1     @hello = "pavan"   end end  h = Hello.new p h.instance_variable_get(:@hello) #nil p h.method1                        #"pavan" - initialization of @hello p h.instance_variable_get(:@hello) #"pavan" 

If the variable is undefined (first call of instance_variable_get in my example) you get nil.

---

As Andrew mention in his comment:

You should not make this the default way you access instance variables as it violates encapsulation.

A better way is to define an accessor:

class Hello   def method1     @hello = "pavan"   end   attr_reader :hello   end  h = Hello.new p h.hello #nil p h.method1                        #"pavan" - initialization of @hello p h.hello #"pavan" 

If you want another method name, you could alias the accessor: alias :my_hello :hello.

And if the class is not defined in your code, but in a gem: You can modify classes in your code and insert new functions to classes.

Answer 2

You can also accomplish this by calling attr_reader or attr_accessor like this:

class Hello   attr_reader :hello    def initialize     @hello = "pavan"   end end 

or

class Hello   attr_accessor :hello    def initialize     @hello = "pavan"   end end 

Calling attr_reader will create a getter for the given variable:

h = Hello.new p h.hello        #"pavan" 

Calling attr_accessor will create a getter AND a setter for the given variable:

h = Hello.new p h.hello        #"pavan" h.hello = "John" p h.hello        #"John" 

As you might understand, use attr_reader and attr_accessor accordingly. Only use attr_accessor when you need a getter AND a setter and use attr_reader when you only need a getter