ivar_assign.rb

class Module
  def method_default(*method_names)
    method_names.each do |name|
      method = instance_method(name)

      ivars = method.parameters.map { |type, name| "@#{name}" }

      define_method(name) do |*args, &block|
        ivars.zip(args) do |name, arg|
          instance_variable_set name, arg
        end

        method.bind(self).call(*args, &block)
      end
    end
  end
end

class Foo
  def initialize(foo, bar, baz)
    p @foo, @bar, @baz
  end
  method_default :initialize
end

Foo.new(3, 4, 5)