Need to type a function using $Subtype and generics

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Need to type a function using $Subtype and generics



I’m trying to use $Subtype to type a mixin function. I believe my type signature is correct. I keep getting some errors:


$Subtype


const MyMixin: MixinFunction = superclass => class extends superclass ;
^ Cannot extend `superclass` [1] with
`<<anonymous class>>` because `A` [2] is
not inheritable.



Here is my super simple code (on Try Flow):


type MixinFunction = <A>(superclass: Class<A>) => Class<$Subtype<A>>;

const MyMixin: MixinFunction = superclass => class extends superclass ;



How can I made this code work without errors?









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