strictFunctionTypes option should strictly check callback parameters of override methods #19007

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1. ahejlsberg commented on Oct 7, 2017

   

   Anders Hejlsberg (ahejlsberg)

   on Oct 7, 2017

   Member

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   This is working as intended. As explained here, in --strictFunctionTypes mode we still check parameters of methods and constructors bivariantly. So, there is no error here:

   interface C {
     a(f: (a: C) => C): void;
   }
   interface D extends C {
     p: boolean;
     a(f: (a: D) => D): void;
   }

   But an error is reported here:

   interface C {
     a: (f: (a: C) => C) => void;
   }
   interface D extends C {
     p: boolean;
     a: (f: (a: D) => D) => void;
   }

   As I explain here, we can't tighten this any further without causing Array<T> and other core types to become invariant.
2. Anders Hejlsberg (ahejlsberg)

   added

   Working as IntendedThe behavior described is the intended behavior; this is not a bugThe behavior described is the intended behavior; this is not a bug

   on Oct 7, 2017
3. falsandtru commented on Oct 7, 2017

   

   falsandtru (falsandtru)

   on Oct 7, 2017

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   I see, thanks for your explanation.
4. microsoft

   locked and limited conversation to collaborators on Jun 14, 2018