declaration: Namespace which exports class can't be merged with variable #13536

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1. aluanhaddad commented on Jan 17, 2017

   

   Aluan Haddad (aluanhaddad)

   on Jan 17, 2017

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   Note that the GotApi interface is not exported
2. ikokostya commented on Jan 17, 2017

   

   ikokostya

   on Jan 17, 2017

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   Note that the GotApi interface is not exported

   How interface should be exported? This code (similar to request declaration) also isn't compiled with the same error:

   declare namespace got {
       export interface GotApi {
           (): any;
           delete(): any;
       }
   
       export class HTTPError {}
   }
   
   declare var got: got.GotApi;
   export = got;

   If remove class export from namespace, compilation is completed:

   interface GotApi {
       (): any;
       delete(): any;
   }
   
   declare var got: GotApi;
   
   declare namespace got {
       // export class HTTPError extends Error {} <--- Comment this line
   }
   
   export = got;
3. mhegazy commented on Jan 17, 2017

   

   Mohamed Hegazy (mhegazy)

   on Jan 17, 2017

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   Ideally this would be rewitten as function+namespace but it can not, #1784 (and #9846) track that.

   Instantiated namespaces (i.e. ones that has a value in them) can not merge with variables, since one of them will override the other at run-time.

   you can write your declaration as such:

   declare class HTTPError { }
   
   interface GotApi {
       (): any;
       delete(): any;
       HTTPError: typeof HTTPError;
   }
   
   declare var got: GotApi;
   export = got;
4. Mohamed Hegazy (mhegazy)

   added

   DuplicateAn existing issue was already createdAn existing issue was already created

   on Jan 17, 2017
5. ikokostya commented on Jan 17, 2017

   

   ikokostya

   on Jan 17, 2017

   Last edited by ikokostya

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   Instantiated namespaces (i.e. ones that has a value in them) can not merge with variables, since one of them will override the other at run-time.

   As I understand from documentation about declaration merging function and variable are value creating declarations, i.e. code

   interface GotApi {
       (): any;
   }
   declare var got: GotApi;
   declare namespace got {
       export class HTTPError {}
   }
   export = got;

   and

   declare var got: () => any;
   declare namespace got {
       export class HTTPError {}
   }
   export = got;

   fails to compile. But function declaration is compiled:

   declare function got(): any;
   declare namespace got {
       export class HTTPError {}
   }
   export = got;

   Why this happen?

   Also, I propose to make error message is more detailed, because current message error TS2300: Duplicate identifier 'got'. is cryptic at first glance. For example, namespace and variable declaration can't be merged.
6. mhegazy commented on Jan 17, 2017

   

   Mohamed Hegazy (mhegazy)

   on Jan 17, 2017

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   var got: ()=> any is treated as a variable, and not as a function declaration. the reason is a variable can be assigned to later on where as a function can not.
7. ikokostya commented on Jan 17, 2017

   

   ikokostya

   on Jan 17, 2017

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   Mohamed Hegazy (@mhegazy) Thanks for explanation.
8. ikokostya

   closed this as completedon Jan 17, 2017
9. BendingBender commented on Jul 22, 2017

   

   Dimitri B. (BendingBender)

   on Jul 22, 2017

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   Mohamed Hegazy (@mhegazy) So why is it then not allowed to merge a declare const with a declare namespace? AFAIK, const is also not assignable more than once.

   👍React with 👍1Reacted by Georgii Dolzhykov
10. microsoft

    locked and limited conversation to collaborators on Jun 19, 2018