Demonstration of changing the behavior of ruby's `rescue` so that it only handles shallow exceptions raised in directly called methods. Note that a bare `rescue` won't work with this, unfortunately. See https://twitter.com/garybernhardt/status/229323716

output

$ ruby --version
ruby 1.9.3p194 (2012-04-20 revision 35410) [x86_64-darwin11.4.0]
$ ruby shallow_exceptions.rb 
Exception handled: shallow exception
shallow_exceptions.rb:13:in `raise_shallow_exception': deep exception (StandardError)
	from shallow_exceptions.rb:17:in `raise_deep_exception'
	from shallow_exceptions.rb:27:in `try_handle_deep_exception'
	from shallow_exceptions.rb:34:in `<main>'

shallow_exceptions.rb

def Exception.===(exception)
  # verify the main part of the backtrace matches...
  return false unless (exception.backtrace[1..-1] == caller[1..-1])

  # verify the rescue is in the same method as the caller of the method that raised.
  caller_of_method_that_raised = exception.backtrace[1][/:\d+:in `([^']+)'\z/, 1]
  rescuer = caller[0][/:\d+:in `(?:rescue in )?([^']+)'\z/, 1]

  caller_of_method_that_raised == rescuer
end

def raise_shallow_exception(msg = "shallow exception")
  raise StandardError, msg
end

def raise_deep_exception
  raise_shallow_exception "deep exception"
end

def handle_shallow_exception
  raise_shallow_exception
rescue StandardError => e
  puts "Exception handled: #{e.message}"
end

def try_handle_deep_exception
  raise_deep_exception
rescue StandardError => e
  # this won't be triggered
  puts "Exception handled: #{e.message}"
end

handle_shallow_exception
try_handle_deep_exception