Strict conversion of enums to F #

Question

I want to write a function with a signature int -> 'TEnumthat will throw an exception if the target enum does not contain an input value. Here is my first attempt:

let parseEnum<'TEnum when 'TEnum : enum<int>> (value : int) : 'TEnum =
    let enumType = typeof<'TEnum>
    if not <| Enum.IsDefined (enumType, value) then
        raise <| ArgumentException (sprintf "Invalid value of %A: %d" enumType value)

    enum value

The compiler shows me the following error message: "error FS0001: parameter of the declared type" TEnum "cannot be used here, because the type parameter cannot be resolved at compile time" (I think because of a function enumthat has an additional restriction).

Okay, okay, I understand the problem. I will use a statically permitted type parameter . Here is my second attempt:

let inline parseEnum2 (value : int) : ^TEnum =
    let enumType = typeof<^TEnum>
    if not <| Enum.IsDefined (enumType, value) then
        raise <| ArgumentException (sprintf "Invalid value of %A: %d" enumType value)

    enum value

: " FS3156: → " typeof<^TEnum>.

? ?

Answer 1

"" ˆ < :

let enumType = typeof< ^TEnum>

, :

open System
let inline parseEnum2 value : 'TEnum =
    let enumType = typeof<'TEnum>
    if not <| Enum.IsDefined (enumType, value) then
        raise <| ArgumentException (sprintf "Invalid value of %A: %d" enumType value)

    enum value

, , "", - .