Smartly unboxes a value from a data reader into various target representations

SmartUnbox.fs

/// Smartly unboxes a nullable value, with different semantics depending on the target type (nullable, option etc...)
let SmartUnbox<'a> isNull (value:obj) : 'a =
    // help from from http://www.fssnip.net/hh
    let targetType = typeof<'a>
    let typeFlavour = TypeFlavour.Create<'a>()
    match (isNull,typeFlavour) with
        | true, ValueType -> failwithf "Can't return null for type %s" targetType.Name
        | true, _ -> (box null) :?> 'a // cast null to nullable/option/reference type works fine!
        | false, OptionT t ->
                // Have to create the 'Some' member via reflection
                targetType.GetMethod("Some").Invoke(null, [| value |]) :?> 'a
        | false, _ -> value |> unbox