How to downcast from obj to option?

Question

I have a function that takes a parameter of type object and needs to downcast it to an option.

member s.Bind(x : obj, rest) =
    let         


        

Answer 1

To answer your last question: you can use a slight variation of Tomas' code if you need a general-purpose way to check for options without boxing values beforehand:

let (|Option|_|) value = 
  if obj.ReferenceEquals(value, null) then None
  else
    let typ = value.GetType()
    if typ.IsGenericType && typ.GetGenericTypeDefinition() = typedefof> then
      let opt : option<_> = (box >> unbox) value
      Some opt.Value
    else None
//val ( |Option|_| ) : 'a -> 'b option    

let getValue = function
  | Option x ->  x
  | _ -> failwith "Not an option"

let a1 : int = getValue (Some 42)
let a2 : string = getValue (Some "foo")
let a3 : string = getValue (Some 42) //InvalidCastException
let a4 : int = getValue 42 //Failure("Not an option")