Question

class Appointment
  def self.listen_to(*methods)
    methods.each do |method_sym|
      mth = method(method_sym) # <- doesn't find method `something`
      define_method(method_sym) do
        print "<listen>#{mth.call}</listen>"
      end
    end
  end

  def something
    print "doing something"
  end

  listen_to :something
end

Undefined method 'something' for class 'Class'. The problem seems to be that method(:somesymbol) looks in the class’s scope, and not in the instance scope for the method.

How can I access the something-method from within the def self.listen_to-classmethod?

Answer 1

You need to use instance_method, not method:

mth = instance_method(method_sym)

Not part of the question, but the means of wrapping the method will be a bigger issue. I’d use alias_method to rename the old method, and use send to call it.

> class Appointment
*   def self.listen_to(*methods)  
*     methods.each do |sym|    
*       new_sym = "__orig_#{sym}".to_sym      
*       alias_method new_sym, sym      
*       mth = instance_method(sym) # <- doesn't find method `something`      
*       define_method(sym) do      
*         "<listen>#{send new_sym}</listen>"        
*       end        
*     end      
*   end    
*   
*   def something  
*     "doing something"    
*   end    
*   
*   listen_to :something  
* end  
> puts Appointment.new.something
<listen>doing something</listen>