type Foo () = class end
type Bar () = inherit Foo ()
 
type FooCollection () = class end // not really necessary
 
type Test1 () =
  static member AddRange (col: FooCollection) = () // could be an int or anything instead
  static member AddRange (foos: Foo []) = ()
 
type Test2 () = static member AddRange (foos: Foo []) = ()
 
// won't compile
//Test1.AddRange [|Bar ()|] // error: have to explicitely cast => [|Bar () :> Foo|]
 
Test2.AddRange [|Bar ()|] // works
 

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