Executing code for every method call in a Ruby module

Question

I'm writing a module in Ruby 1.9.2 that defines several methods. When any of these methods is called, I want each of them to execute a certain statement first.

module MyModule   def go_forth     a re-used statement     # code particular to this method follows ...   end    def and_multiply     a re-used statement     # then something completely different ...   end end 

But I want to avoid putting that a re-used statement code explicitly in every single method. Is there a way to do so?

(If it matters, a re-used statement will have each method, when called, print its own name. It will do so via some variant of puts __method__.)

Answer 1

Like this:

module M   def self.before(*names)     names.each do |name|       m = instance_method(name)       define_method(name) do |*args, &block|           yield         m.bind(self).(*args, &block)       end     end   end end  module M   def hello     puts "yo"   end    def bye     puts "bum"   end    before(*instance_methods) { puts "start" } end  class C   include M end  C.new.bye #=> "start" "bum" C.new.hello #=> "start" "yo" 

Answer 2

This is exactly what aspector is created for.

With aspector you don't need to write the boilerplate metaprogramming code. You can even go one step further to extract the common logic into a separate aspect class and test it independently.

require 'aspector'  module MyModule   aspector do     before :go_forth, :add_multiply do       ...     end   end    def go_forth     # code particular to this method follows ...   end    def and_multiply     # then something completely different ...   end end