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 
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3 Answers
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.
6 Comments
Andrew Marshall
You should not make this the default way you access instance variables as it violates encapsulation.
nik7
@knut can't we just do this like
h = Hello.new and h.method1 and h.hello ?
knut
@nlingutla You can define an accessor with
attr_reader :hello
baash05
For me, this is great for specs, where you don't want to make something public.
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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
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In case anyone wants to access the variable to set, here how they can do it:
puts h.instance_variable_get(:@hello) # nil h.instance_variable_set(:@hello, "StackOverflow") # <- set the value puts h.instance_variable_get(:@hello) # StackOverflow 