From: "shugo (Shugo Maeda)" <redmine@...>
Date: 2013-01-16T17:39:41+09:00
Subject: [ruby-core:51466] [ruby-trunk - Bug #7696] Lazy enumerators with state can't be rewound


Issue #7696 has been updated by shugo (Shugo Maeda).


marcandre (Marc-Andre Lafortune) wrote:
> 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.

#7691 is the basically same issue as #6142.

Do you have a draft API spec in mind?
It might be too late to introduce a new API, though.

----------------------------------------
Bug #7696: Lazy enumerators with state can't be rewound
https://bugs.ruby-lang.org/issues/7696#change-35444

Author: marcandre (Marc-Andre Lafortune)
Status: Open
Priority: High
Assignee: 
Category: core
Target version: 2.0.0
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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