Issue #21040 has been updated by Hanmac (Hans Mackowiak). These are called `virtual variables`, a new object is created each time you try to access it ```c rb_define_virtual_variable("$~", get_LAST_MATCH_INFO, match_setter); rb_define_virtual_variable("$&", last_match_getter, 0); rb_define_virtual_variable("$`", prematch_getter, 0); rb_define_virtual_variable("$'", postmatch_getter, 0); rb_define_virtual_variable("$+", last_paren_match_getter, 0); ``` in ruby this is the result: ```ruby "123".gsub(/.../){ p [$&, $&.object_id, #=> 30 $&.object_id #=> 40 ] } ``` ---------------------------------------- Bug #21040: String#next! method does not mutate $& variable https://bugs.ruby-lang.org/issues/21040#change-111533 * Author: radarek (Radosław Bułat) * Status: Rejected * ruby -v: ruby 3.4.1 (2024-12-25 revision 48d4efcb85) +PRISM [arm64-darwin24] * Backport: 3.1: UNKNOWN, 3.2: UNKNOWN, 3.3: UNKNOWN, 3.4: UNKNOWN ---------------------------------------- `String#next!` method should mutate string and return mutated version. For some reason, using it on `$&` does not mutate it but still returns new version. Steps to reproduce (2 different ways): ```ruby "123".gsub(/./){$&.next!} # returns "234" as expected "123".gsub(/./){$&.next!;$&} # returns "123" but should be "234" "123".gsub(/./){_1.next!;_1} # returns "234" as expected "123"[/./] puts $&. # prints 1 puts $&.next! # prints 2 puts $& # prints 1 but should be 2 ``` -- https://bugs.ruby-lang.org/