Possible for a module included somewhere to override a class's instance method?

hack.rb

class Base
  def call
    'call'
  end
end

p Base.new.call  #=> "call"


# Monkeypatching "works" but doesn't provide access to #super
class Base
  def call
    'monkeypatched'
  end
end

module Prepending
  def append_features(base)
    return super unless base.is_a? Class
    prepend = self
    base.extend Module.new { define_method(:new) { |*| super.extend(prepend) }}
  end
end

p Base.new.call  #=> "monkeypatched"

# This is the spirit of what I'd like, but methods defined on the class will be
# preferred over those in ancestors.
module Override
  extend Prepending
  def call
    [ 'overridden', super ]
  end
end

class Base
  include Override
end

p Base.new.call  #=> ["overridden", "monkeypatched"]



# This works but I don't have access to the class instances to apply this method.
instance = Base.new
class << instance
  def call
    [ 'overridden', super ]
  end
end
p instance.call  #=> ["overridden", ["overridden", "monkeypatched"]]

What's "_" in base.extend Module.new { define_method(:new) { |_| super.extend(prepend) }}?

Shouldn't it look like this instead? base.extend Module.new { define_method(:new) { |*args| super(*args).extend(prepend) }}

No, |*| is a shorthand syntax for I don't care about the arguments. super without args and parens will automatically send any arguments passed to the original call and a block, if there is one (missing from your code). So { |*| super } is equivalent to { |*args, &block| super(*args, &block) }.

👍 thanks!