Issue #7696 has been updated by marcandre (Marc-Andre Lafortune).


Oh oh.

Let me add a third example to problems of handling states:

    e = (1..6).lazy.drop(3)
    e.flat_map{e}.force # => [(1..6)]*3, should be  [(1..3)]*3

I believe only the first solution would work for this.


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Bug #7696: Lazy enumerators with state can't be rewound
https://bugs.ruby-lang.org/issues/7696#change-35450

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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