Is it possible to run code after each line in Ruby?

Question

I understand that it is possible to decorate methods with before and after hooks in ruby, but is it possible to do it for each line of a given method?

For example, I

Answer 1

It sounds like you want tracing on every method call on every object, but only during the span of every call to one particular method. In that case, you could just redefine the method to turn on- and off instrumentation. First, use the universal instrumentation suggsted in Pinochle's answer, then redefine the method in question as follows:

# original definition, in /lib/foo.rb:
class Foo
  def bar(baz)
    do_stuff
  end
end

# redefinition, in /test/add_instrumentation_to_foo.rb:
Foo.class_eval do
  original_bar = instance_method(:bar)
  def bar(baz)
    TracedObject.install!
    original_bar.bind(self).call(baz)
    TracedObject.uninstall!
  end
end

You'd need to write the install! and uninstall methods, but they should be pretty trivial: just set or unset a class variable and check for it in the instrumentation logic.