[ruby-core:121617] [Ruby Bug#21260] duping stringio objects shares cursors
From:
"jeremyevans0 (Jeremy Evans) via ruby-core" <ruby-core@...>
Date:
2025-04-10 05:46:27 UTC
List:
ruby-core #121617
Issue #21260 has been updated by jeremyevans0 (Jeremy Evans).
This is how `IO#dup` works. What would be the benefit of `StringIO#dup` behaving differently?
```ruby
f = File.open('filename.rb')
f2 = f.dup
f2.pos # => 0
f.read 4
f2.pos # => 4
```
----------------------------------------
Bug #21260: duping stringio objects shares cursors
https://bugs.ruby-lang.org/issues/21260#change-112669
* Author: chucke (Tiago Cardoso)
* Status: Open
* ruby -v: ruby 3.4.2 (2025-02-15 revision d2930f8e7a) +PRISM [x86_64-darwin23]
* Backport: 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN
----------------------------------------
I've found that, if I `.dup` a stringio, when I read one of the objects, the cursor also moves internally on the other:
```ruby
require "stringio"
s1 = StringIO.new("test")
s2 = s1.dup
s1.read #=> "test"
s2.read #=> ""
s1.rewind
s2.rewind
s2.read #=> "test"
s1.read #=> ""
s1.pos #=> 4
s2.pos #=> 4
```
--
https://bugs.ruby-lang.org/
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