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Create getter and setter on a valorized variable

Posted by Sandro Paganotti in Ruby on Rails - 3 comments

I noticed that none of the attr_* (attr_reader, attr_accessor and attr_writer) has the capability to let you assign a value to the variable you’re creating.

This can be solved using the Class constructor method but it can lead you to define the initialize function just to make these assignements.

So I created an attr_with_value method that can be added to the Object class in order to make it avaiable to all the Classes and that can let you use the following sintax:

class Printer
  attr_with_value :pippo, 5
  attr_with_value :printer, Proc.new{|a| p "saying: #{a}" }
end

pr = Printer.new
pr.printer.call("hello!")
# "saying: hello!" 
p pr.pippo
# 5

pr.printer = Proc.new{|a| p "whispering #{a}"}
pr.printer.call("hello!")
# "whispering hello!" 

In the following snippet you can find the method:

class Object
  def self.attr_with_value(name,value)

    class_eval <<-EOS

      define_method(name.to_s) do      
        @#{name}_starter.nil? ? value : @#{name} 
      end

      define_method(name.to_s+"=") do |val|
        @#{name}_starter = true; @#{name} = val
      end

    EOS

  end  
end

I’m looking for a way to improve it (in particular I’m trying to find a clever way to handle the initial assignment), so every suggestion is welcome!

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