Function overload breaks generics #29312

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1. wKich commented on Jan 9, 2019

   

   Dmitriy Lazarev (wKich)

   on Jan 9, 2019

   Last edited by wKich

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   I have same issue in another example (TypeScript version: 3.2.2)

   function foo(a: number, b: string): void;
   function foo(a: string): void;
   
   function foo(a: string | number, b?: string) {}
   
   foo.call(null, 1, "2"); // Expected 2 arguments, but got 3.
   foo.bind(null)(1, "2"); // Expected 1 arguments, but got 2.
   foo.apply(null, [1, "2"]); // Type 'number' is not assignable to type 'string'.
   
   foo.call(null, "2"); // no errors
   foo(1, "2"); // no errors
   foo("2"); // no errors

   So I can't use call/bind/apply with overloaded functions.

   Update: Sorry, I didn't see #27028 (comment)
2. Wesley Wigham (weswigham)

   added

   Needs InvestigationThis issue needs a team member to investigate its status.This issue needs a team member to investigate its status.

   on Jan 10, 2019
3. Bludator commented on Mar 3, 2019

   

   Bludator

   on Mar 3, 2019

   Last edited by Bludator

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   I have yet another example:

   function Wrap<O extends (...any) => any>(a: O, params: Parameters<O>): void { }
   
   let Bar: {
       Foo<K extends "FooBar">(a: K, b: number): void;
       //comment out this ↓ line:
       Foo(a: never): never;
   };
   
   //This should work:
   Wrap(Bar.Foo, ["FooBar", 78])

   link to playground.
4. jack-williams commented on Mar 3, 2019

   

   Jack Williams (jack-williams)

   on Mar 3, 2019

   Collaborator

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   Bludator That is a separate issue linked to the design of conditional type inference. When inferring from an overloaded function the last overload is always picked, so Parameters just picks up the last case which happens to be never.

   See #21496

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

   added

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

   and removed

   Needs InvestigationThis issue needs a team member to investigate its status.This issue needs a team member to investigate its status.

   on Jul 23, 2019
6. RyanCavanaugh commented on Jul 23, 2019

   

   Ryan Cavanaugh (RyanCavanaugh)

   on Jul 23, 2019

   Member

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   Inference only works with the last overload
7. Ryan Cavanaugh (RyanCavanaugh)

   closed this as completedon Jul 23, 2019