[ruby-core:24520] Proposal: savepoints

Matz,
I have been thinking a lot about trying to find a way to make it easier to
implement code reloading in Ruby. Rails already implements code reloading
using remove_const, undef, etc., but it's fairly messy and can produce
problems. It's also a fair bit of code to implement.

I was thinking that the addition of a simple feature would make this a lot
easier to do in Ruby: savepoints. It would work like this:

class Foo
end

sp = ObjectSpace.savepoint

class Bar
end

bar = Bar.new

sp.rollback

Foo #=> Foo
Bar #=> nil (or RefError)
bar #=> nil (or RefError)

Then, if we load the files again, we should get a reliable new set of
classes. This feature would only be used in development, single-threaded
mode, and in isolated scenarios (the user changed a file--next time the user
requests a page, roll back the savepoint and reload the user's classes).

I am unsure what the correct solution is, but having a more explicit way in
Ruby to handle class reloading (which we already do in Rails, and it's an
important feature) would be very helpful.

-- 
Yehuda Katz
Developer | Engine Yard
(ph) 718.877.1325