Issue #19632 has been updated by matz (Yukihiro Matsumoto). `peek` does not seem to modify the enumerator? Should we prohibit it (or not)? ---------------------------------------- Bug #19632: Disable external iterator for frozen enumerator https://bugs.ruby-lang.org/issues/19632#change-103046 * Author: make_now_just (Hiroya Fujinami) * Status: Open * Priority: Normal * Backport: 3.0: UNKNOWN, 3.1: UNKNOWN, 3.2: UNKNOWN ---------------------------------------- Currently, methods to manipulate an external iterator like `#next` and `#feed` can be called even if a receiver of an enumerator is frozen. However, these methods change the state of an external iterator in an enumerator. Therefore, it seems a BUG to me, and these methods should raise FrozenError if the receiver is frozen. ```ruby e = 3.times.freeze # Current e.next # => 1 e.next # => 2 # Expected e.next # raise FrozenError ``` Two years ago, this issue was mentioned in [a comment](https://bugs.ruby-lang.org/issues/17195#note-5). I suggest fixing the following methods to raise FrozenError against a frozen enumerator. - `Enumerator#next` - `Enumerator#next_values` - `Enumerator#peek` - `Enumerator#peek_values` - `Enumerator#feed` - `Enumerator#rewind` Also, even if an enumerator is frozen, it does not affect other methods for internal iterators. -- https://bugs.ruby-lang.org/