CODEWITHSUNDEEP
ruby
dhulihan
dhulihan

Reputation: 11293

Dynamically Create Class Attributes with attr_accessor

In Ruby, is there a way to dynamically add a instance variable to a class? For Example:

class MyClass

  def initialize
    create_attribute("name")
  end 

  def create_attribute(name)
    attr_accessor name.to_sym
  end

end

o =  MyClass.new
o.name = "Bob"
o.name

Upvotes: 9

Views: 9166

Answers (3)

MatzFan
MatzFan

Reputation: 937

Made a mess of answering @ericso's comment/question in another comment, so here it is in an answer - a module which I use (based on @ReeseMoore's code) to do this & set instance vars, if necessary:

# adds ability to dynamically create instance vars & attr_accessors
module Attributable
  def create_method(name, &block)
    self.class.send(:define_method, name.to_sym, &block)
  end

  def create_setter(m)
    create_method("#{m}=".to_sym) { |v| instance_variable_set("@#{m}", v) }
  end

  def create_getter(m)
    create_method(m.to_sym) { instance_variable_get("@#{m}") }
  end

  def set_attr(method, value)
    create_setter method
    send "#{method}=".to_sym, value
    create_getter method
  end
end

Upvotes: 0

psjscs
psjscs

Reputation: 531

maybe ,

instance_variable_set(name,value)

is what your want!

eg:

class Mclass
  def show_variables
    puts self.class.instance_variables
  end
end

Mclass.instance_variable_set(:@test,1)
o=Mclass.new
o.show_variables

you know, class is object too.

Upvotes: 1

Reese Moore
Reese Moore

Reputation: 11640

One way (there are others) is to use instance_variable_set and instance_variable_get as so: 

class Test
    def create_method( name, &block )
        self.class.send( :define_method, name, &block )
    end

    def create_attr( name )
        create_method( "#{name}=".to_sym ) { |val| 
            instance_variable_set( "@" + name, val)
        }

        create_method( name.to_sym ) { 
            instance_variable_get( "@" + name ) 
        }
    end
end

t = Test.new
t.create_attr( "bob" )
t.bob = "hello"
puts t.bob

Upvotes: 27

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