Bug #8815: Enumerable.drop_while returns an Enumerator. Calling next twice on the Enumerator raises StopIteration even if there are still items available

• Status: Rejected
• Assignee: -
• Target version: -
• ruby -v: ruby 2.0.0p247 (2013-06-27 revision 41674) [x86_64-darwin12.3.0]
• Backport: 1.9.3: UNKNOWN, 2.0.0: UNKNOWN

[ebouchut (Eric Bouchut)]

I have an enumerable (array) that contains 3 items
[1, 2, 3].
I send drop_while without a block to this array to get an Enumerator.
enumerator = [1, 2, 3].drop_while

When I call next twice on the Enumerator
enumerator.next # => 1
enumerator.next # => raises StopIteration
The second call enumerator.next raises StopIteration whereas the Enumerable contains more than one item.

I expected the second call to enumerator.next to return 2 instead.

I reproduced this on:

• ruby-1.9.3-p448
• ruby-2.0.0-p247
• rbx-2.0.0
  However it works fine in 1.8.7, even if 1.8.7's documentation did not mention about Enumerable.drop_while returning an Enumerator.

Here is an RSpec example that isolates the problem:
http://preview.tinyurl.com/enumerable-drop-while

Eric

[nobu (Nobuyoshi Nakada)]

• Status changed from Open to Rejected

Not a bug.

Enumerable#drop_while stops if the block returns false (or nil).
You have to feed true value to the enumerator by Enumerator#feed.

enumerator.next # => 1
enumerator.feed(true)
enumerator.next # => 2

[JEG2 (James Gray)]

Isn't that backwards?

>> [1, 2, 3].drop_while { nil }
=> [1, 2, 3]
>> [1, 2, 3].drop_while { false }
=> [1, 2, 3]
>> [1, 2, 3].drop_while { true }
=> []