From: Lars Olsson <lasso@...>
Date: 2009-09-22T17:45:06+09:00
Subject: Monkeypatching multiple classes with similar methods

Hello!

I'm trying to monkeypatch a number of related classes that all
implements the same method (meth). The methods all take one required
argument (stuff) but some of the individual methods may require more
arguments (or a block). All I want to do in each call to meth is to
print some debug data and then pass the incoming arguments to the
original method. This works great as long as I know the exact number
of arguments required, but when the number of arguments starts to
change my code breaks badly. Is there any way (in ruby 1.8.7) to
"copy" the original method signature when defining my own replacement
method?

/lasso

--- CODE START ---
class Klass1
  def meth(stuff)
    puts "You've sent #{stuff} to #{self.class}.meth"
  end
end

class Klass2
  def meth(stuff, &block)
    block_text = block_given? ? 'with' : 'without'
    puts "You've sent #{stuff} to #{self.class}.meth #{block_text} a
block"
  end
end

class Klass3
  def meth(stuff, morestuff)
    puts "You've sent #{stuff} to #{self.class}.meth"
  end
end

# Broken monkeypatching. Only works on Klass1
[Klass1, Klass2, Klass3].each do |klass|
  klass.module_eval do
    alias_method :original_meth, :meth
    def meth(stuff)
      puts "#{self.class}.meth has been patched"
      original_meth(stuff)
    end
  end
end

Klass1.new.meth('one')
Klass2.new.meth('two') { 'three' } # Block is not passed after
monkeypatching
Klass2.new.meth('four')
Klass3.new.meth('five', 'six') # Raises ArgumentError after
monkeypatching
--- CODE END ---