From: matz@...
Date: 2015-10-21T12:48:27+00:00
Subject: [ruby-core:71133] [Ruby trunk - Feature #11498] Kernel#loop: return the "result" value of StopIteration

Issue #11498 has been updated by Yukihiro Matsumoto.


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

Matz.


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Feature #11498: Kernel#loop: return the "result" value of StopIteration
https://bugs.ruby-lang.org/issues/11498#change-54505

* Author: Akinori MUSHA
* Status: Open
* Priority: Normal
* Assignee: Yukihiro Matsumoto
----------------------------------------
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.

---Files--------------------------------
loop-result.patch (3.03 KB)


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