Question

What i bascially want is to extend the Numeric class so that it has one extra Attribute (currencie), which is set when of the undefined methods are invoked [yen(s), euro(s), etc.]
So, here is the class definition:

 class Numeric

 @@currencies = {'yen' => 0.013, 'euro' => 1.292, 'rupee' => 0.019, 'dollar' => 1}

 attr_accessor :currencie

 def method_missing(method_id)
   singular_currency = method_id.to_s.gsub( /s$/, '')
   if @@currencies.has_key?(singular_currency)
    self.currencie = singular_currency
    self * @@currencies[singular_currency]
    puts "method finished"
   else
    super
   end
 end

 def in(convert_to) 

 end

end

Now, when i run the code

a = 5.rupees
puts "currencie is -> " + a.currencie

i’ve got:

method finished
/path_to_file/hw2.1.rb:33:in `<main>': undefined method `currencie' for nil:NilClass (NoMethodError) 

Also the attribute currencie seems to be unset.

What am i doing wrong ?

Answer 1

In your case method_missing should return object i.e. self. Just add self to method_missing and it will work.

def method_missing(method_id)
   singular_currency = method_id.to_s.gsub( /s$/, '')
   if @@currencies.has_key?(singular_currency)
    self.currencie = singular_currency        
    puts "method finished"
    self * @@currencies[singular_currency] # just change the order of expressions
   else
    super
   end
 end

EDIT: Fixed as injekt said