Enums does not support literal typing with computed values #27976

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1. ahejlsberg commented on Oct 19, 2018

   

   Anders Hejlsberg (ahejlsberg)

   on Oct 19, 2018

   Member

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   This is still a design limitation. For mostly historical reasons we have two fundamentally different kinds of enums in the language, numeric and literal. Numeric enums are just like the number type, except that distinct numeric enums are not assignable to each other. Literal enums are quite different: Each enum member has a distinct unit type, and the enum type itself is a union of the enum member types. As described in #9407, we distinguish between the two based on how the members are declared:

   When each member of an enum type has either an automatically assigned value, an initializer that specifies a numeric literal, or an initializer that specifies a single identifier naming another enum member, that enum type is considered a union (a.k.a. literal) enum type.

   We chose to do it this way such that we didn't have to introduce an explicit modifier to choose between the two kinds. This still holds. The only way I can see us allowing computed constant expressions for literal enum members is to introduce a modifier, e.g. literal enum E { ... }. But I'm not crazy about that idea.
2. Ryan Cavanaugh (RyanCavanaugh)

   added

   Design LimitationConstraints of the existing architecture prevent this from being fixedConstraints of the existing architecture prevent this from being fixed

   on Oct 19, 2018
3. lukeramsden commented on May 18, 2021

   

   Luke Ramsden (lukeramsden)

   on May 18, 2021

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   Is there any chance of revisiting this? This would allow for composition of enums. My use case is this, as part of an integration with the HubSpot CRM where booleans are passed as "yes"/"no":

   // either
   export enum HubspotBool {
     True = 'yes',
     False = 'no',
   }
   // or
   export const HUBSPOT_TRUE = 'yes';
   export const HUBSPOT_FALSE = 'no';
   
   // doesn't matter which
   
   export enum CustomerIdentityCheckStatus {
     Completed = HubspotBool.True, // fails
     NotCompleted = HUBSPOT_FALSE, // fails
     Failed = 'failed',
   }

   I know it's not super necessary but it's the sort of thing I would expect to "just work", where as currently it gives me an unexpected error which leads me here.

   👍React with 👍63Reacted by Vanley, Ethan Matthews, Onwuka Gideon, Filip Čulig, Richard Waller, BHuber-PlanB, xxxKOTxxx, IhorKulikovskyi, Abhijeet Singh, Camille Drapier and 53 more
4. Anders Hejlsberg (ahejlsberg)

   added this to the TypeScript 5.0.0 milestone on Oct 17, 2022
5. TypeScript Bot (typescript-bot)

   added

   Fix AvailableA PR has been opened for this issueA PR has been opened for this issue

   on Oct 17, 2022
6. Anders Hejlsberg (ahejlsberg)

   closed this as completedin #50528on Nov 3, 2022
7. clockwiser commented on Jan 9, 2023

   

   clockwiser

   on Jan 9, 2023

   Last edited by clockwiser

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   In the typescript documents, it says each enum member has a value associated with it which can be either constant or computed.
   https://www.typescriptlang.org/docs/handbook/enums.html

   enum FileAccess {
   // constant members
   None,
   Read = 1 << 1,
   Write = 1 << 2,
   ReadWrite = Read | Write,
   // computed member
   G = "123".length,
   }

   But the computed doesn't work as the documents described, and throws an error in Vue3 SFC.
   TS2535: Enum type has members with initializers that are not literals.

   👍React with 👍1Reacted by Abhijeet Singh
8. sisiea commented on Feb 10, 2023

   

   Xinghai Zhang (sisiea)

   on Feb 10, 2023

   Last edited by sisiea

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   In the typescript documents, it says each enum member has a value associated with it which can be either constant or computed. https://www.typescriptlang.org/docs/handbook/enums.html

   enum FileAccess { // constant members None, Read = 1 << 1, Write = 1 << 2, ReadWrite = Read | Write, // computed member G = "123".length, }

   But the computed doesn't work as the documents described, and throws an error in Vue3 SFC. TS2535: Enum type has members with initializers that are not literals.

   It's ok that you can define the numeric enum "FileAccess" which has both computed and constant members. However, if you want to use the enum member as a type, the members of the numeric enum must be initialized by literal.

   const num = 1;
   // it‘s ok
   enum UserResponse {
     // constant member 
     No = 0,
     // computed member
     Yes = num,
     // constant member 
     NotSure = 1 + 1
   }
   
   // throws an error  : Enum type has members with initializers that are not literals
   type aType = UserResponse.Yes;
   // throws an error  : Enum type has members with initializers that are not literals
   type bType = UserResponse.NotSure;
   
   
   
   // it‘s ok
   enum UserResponse_1 {
     // constant member initialized by literal
     No = 0,
     // constant member initialized by literal
     Yes = 1,
      // constant member initialized by literal
     NotSure = 2,
   }
   
   // it's ok
   type aType_1 = UserResponse_1.Yes;
   type bType_1 = UserResponse_1.NotSure;

   In addition, this problum has been resolved in 5.0.

   👍React with 👍3Reacted by Elroy Shilling, Rafael Rodrigues and Peter Hostačný