F# Option types Using Option types from C#
Example
It is not a good idea to expose Option types to C# code, as C# does not have a way to handle them. The options are either to introduce FSharp.Core as a dependency in your C# project (which is what you'd have to do if you're consuming an F# library not designed for interop with C#), or to change None values to null.
Pre-F# 4.0
The way to do this is create a conversion function of your own:
let OptionToObject opt =
match opt with
| Some x -> x
| None -> null
For value types you'd have to resort to boxing them or using System.Nullable.
let OptionToNullable x =
match x with
| Some i -> System.Nullable i
| None -> System.Nullable ()
F# 4.0
In F# 4.0, the functions ofObj, toObj, ofNullable, and toNullable where introduced to the Option module. In F# interactive they can be used as follows:
let l1 = [ Some 1 ; None ; Some 2]
let l2 = l1 |> List.map Option.toNullable;;
// val l1 : int option list = [Some 1; null; Some 2]
// val l2 : System.Nullable<int> list = [1; null; 2]
let l3 = l2 |> List.map Option.ofNullable;;
// val l3 : int option list = [Some 1; null; Some 2]
// Equality
l1 = l2 // fails to compile: different types
l1 = l3 // true
Note that None compiles to null internally. However as far as F# is concerned it is a None.
let lA = [Some "a"; None; Some "b"]
let lB = lA |> List.map Option.toObj
// val lA : string option list = [Some "a"; null; Some "b"]
// val lB : string list = ["a"; null; "b"]
let lC = lB |> List.map Option.ofObj
// val lC : string option list = [Some "a"; null; Some "b"]
// Equality
lA = lB // fails to compile: different types
lA = lC // true
