Issue #21260 has been reported by chucke (Tiago Cardoso). ---------------------------------------- Bug #21260: duping stringio objects shares cursors https://bugs.ruby-lang.org/issues/21260 * 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/