Feature #5818: Feature: Raiseable

• Status: Rejected
• Assignee: -
• Target version: -

[kstephens (Kurt Stephens)]

= Proposal

The ability to raise any object that is a Raiseable.

= Problem

• The Exception subclass hierarchy is well-established.
• CRuby does not allow any object that behaves as an Exception to be raised, it must be a subclass of Exception.
• 3rd-party code often rescues Exception; e.g. for error recovery, retry and/or logging.
• Users need the ability to raise objects that would not normally be rescued by any code;
  e.g.: hard timeouts or custom signal handlers in an application.

= Solution

• A "Raiseable" module implements all of the methods currently defined in Exception.
• Exception class includes Raiseable module.
• ruby/eval.c: make_exception() asserts rb_obj_is_kind_of(mesg, rb_mRaiseable),
  instead of rb_obj_is_kind_of(mesg, rb_cException).
• Users should avoid "rescue Raiseable" in usual circumstances.

= Other Ideas not implemented here:

• Remove the obj_is_kind_of(mesg, rb_mRaiseable) restriction to allow pure duck-typing.
• Clean up the ivar names (@bt (Bernd Homuth), @mesg) and method names (set_backtrace).

= Example

(({
raiseable = Class.new do
include Raiseable
def self.exception *args; new *args; end
end

begin
  raise raiseable, "this must be handled"
  assert(false)
rescue Exception
  assert(false)
rescue Raiseable
  assert(true)
end

}))

[kstephens (Kurt Stephens)]

git branch: https://github.com/kstephens/ruby/tree/trunk-raiseable

[matz (Yukihiro Matsumoto)]

Separate the proposal into two: (a) allow non-Exception object to be raised. (b) Raiseable. And I will refuse (b). Currently, I see no good reason for (a), but you can try to persuade me.

Matz.

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Rejected