[ruby-core:44138] [ruby-trunk - Bug #6258][Open] String#succ has suprising behavior for "\u1036" (MYANMAR SIGN ANUSVARA), producing "\u1000" instead of "\u1037"

Issue #6258 has been reported by dbenhur (Devin Ben-Hur).

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Bug #6258: String#succ has suprising behavior for "\u1036" (MYANMAR SIGN ANUSVARA), producing "\u1000" instead of "\u1037"
https://bugs.ruby-lang.org/issues/6258

Author: dbenhur (Devin Ben-Hur)
Status: Open
Priority: Normal
Assignee: 
Category: core
Target version: 
ruby -v: ruby 1.9.3p125, ruby 1.9.2p180,


"\u1036".succ.ord.to_s(16) # => "1000"

Discovered when investigating StackOverflow question http://stackoverflow.com/questions/10020230/anomalous-behavior-while-comparing-a-unicode-character-to-a-unicode-character-range

Range#=== ultimately invokes String#upto which uses String#succ

("\u1036".."\u1037").to_a.map{|c| c.ord.to_s(16)}
=> ["1036"]  # expected ["1036","1037"]

Also once #succ! proceeds past U+1036 it continues to produce U+1000 indefinitely

irb(main):115:0> c = "\u1036"
=> "ဵ"
irb(main):116:0> c.ord.to_s(16)
=> "1035"
irb(main):117:0> c.succ!.ord.to_s(16)
=> "1036"
irb(main):118:0> c.succ!.ord.to_s(16)
=> "1000"
irb(main):119:0> c.succ!.ord.to_s(16)
=> "1000"

But if one starts naturally at U+1000 #succ! increments as expected
irb(main):001:0> c = "\u1000"
=> "က"
irb(main):002:0> c.ord.to_s(16)
=> "1000"
irb(main):003:0> c.succ!.ord.to_s(16)
=> "1001"
irb(main):004:0> c.succ!.ord.to_s(16)
=> "1002"



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