Enum can be assigned out-of-bounds values #30629

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1. dragomirtitian commented on Mar 28, 2019

   

   Titian Cernicova-Dragomir (dragomirtitian)

   on Mar 28, 2019

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   I believe this is by design as stated by Daniel Rosenwasser (@DanielRosenwasser) in #26362 to allow for bitwise operations on flag enums:

   The behavior is motivated by bitwise operations. There are times when SomeFlag.Foo | SomeFlag.Bar is intended to produce another SomeFlag. Instead you end up with number, and you don't want to have to cast back to SomeFlag.
   I think if we did TypeScript over again and still had enums, we'd have made a separate construct for bit flags.
2. jrieken commented on Mar 28, 2019

   

   Johannes Rieken (jrieken)

   on Mar 28, 2019

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   bitwise operations on flag enums:

   That makes sense but then they should geek out and understand that you cannot produce 12 with 1 and/or 2
3. dragomirtitian commented on Mar 28, 2019

   

   Titian Cernicova-Dragomir (dragomirtitian)

   on Mar 28, 2019

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   Johannes Rieken (@jrieken) Challenge accepted 😄 :

   let value: Fonum = Fonum.a << Fonum.b << Fonum.a  |  Fonum.a << Fonum.b; // 12

   I think it is difficult to tell if the resulting number is valid or not if we consider flag enums and the whole range of bitwise operations.

   😄React with 😄2Reacted by Jordi Oliveras Rovira and Sébastien
4. jrieken commented on Mar 28, 2019

   

   Johannes Rieken (jrieken)

   on Mar 28, 2019

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   haha - fair point. There should probably be strict enum that doesn't allow these things...

   👍React with 👍1Reacted by David Hearnden
5. Ryan Cavanaugh (RyanCavanaugh)

   added

   DuplicateAn existing issue was already createdAn existing issue was already created

   on Mar 28, 2019
6. Ryan Cavanaugh (RyanCavanaugh)

   closed this as completedon Mar 28, 2019
7. microsoft

   locked as resolved and limited conversation to collaborators on Oct 21, 2025