Feature #11498: Kernel#loop: return the "result" value of StopIteration

• Status: Closed
• Assignee: matz (Yukihiro Matsumoto)
• Target version: -

[knu (Akinori MUSHA)]

Kernel#loop wraps use of Enumerator rescuing StopIteration raised by Enumerator#next, but it does not provide access to the "result" value of a finished enumerator.
If you wanted to get it, you'd have to rescue StopIteration by yourself.

result = loop {
  begin
    puts enum.next
  rescue StopIteration => exc
    break exc.result
  end
}

This feels awkward when loop is capable of rescuing the exception.

So, my proposal here is to make Kernel#loop return the "result" value, which currently returns nothing (nil).
Kernel#loop takes a "return" of an enumerator (StopIteration) as "break" of a loop, so it should be natural to be able to carry a returned value through to the caller like it was given with "break".

With this enhancement, you could write something like this:

enum = Enumerator.new { |y|
  y << 1
  y << 2
  :ok
}

result = loop {
  puts enum.next
} #=> :ok

Attached is my implementation.

[matz (Yukihiro Matsumoto)]

I like the idea. If anything bad happens by the patch, I'd love to accept this.

Matz.

[knu (Akinori MUSHA)]

• Status changed from Open to Closed

Applied in changeset r52218.

---

Kernel#loop returns the result value of a finished iterator

• vm_eval.c (rb_f_loop): When a loop is stopped by a StopIteration
  exception, return what the enumerator has returned instead of
  nil. [ruby-core:71133] [Feature #11498]