From: "mame (Yusuke Endoh)" <mame@...>
Date: 2013-02-17T15:51:16+09:00
Subject: [ruby-core:52361] [ruby-trunk - Bug #7696][Assigned] Lazy enumerators with state can&#x27;t be rewound


Issue #7696 has been updated by mame (Yusuke Endoh).

Subject changed from Lazy enumerators with state can't be rewound to Lazy enumerators with state can&#x27;t be rewound
Status changed from Open to Assigned
Target version changed from 2.0.0 to next minor


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Bug #7696: Lazy enumerators with state can&#x27;t be rewound
https://bugs.ruby-lang.org/issues/7696#change-36409

Author: marcandre (Marc-Andre Lafortune)
Status: Assigned
Priority: High
Assignee: matz (Yukihiro Matsumoto)
Category: core
Target version: next minor
ruby -v: r38800


The 4 lazy enumerators requiring internal state, i.e. {take|drop}{_while}, don't work as expected after a couple `next` and a call to `rewind`.

For example:

    e=(1..42).lazy.take(2)
    e.next # => 1
    e.next # => 2
    e.rewind
    e.next # => 1
    e.next # => StopIteration: iteration reached an end, expected 2

This is related to #7691; the current API does not give an easy way to handle state.

Either there's a dedicated callback to rewind, or data must be attached to the yielder.


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