F# HashCode to enum conversion

Question

I have an enum of bit-masked error codes with a string representation and an binary int representation:

type ErrorCodes = 
    | NoError = 0
    | InvalidInputError = 1
    | AuthenticationFailedError = 2
    | InvalidArgumentError = 4
    | ItemNotFoundError = 8
    | UnknownError = 16

As I run through the program, I collect all the errors by using the bitwise OR operator (|||). So now I have something that looks like 01100. How can I print to the console: "InvalidArgumentError", and "ItemNotFoundError?"

I had an idea of just using:

for i = 0 to 32 do
    if ((err.GetHashCode() % 2) = 1) then
        Console.WriteLine("ErrorCode: {0}",err.GetHashCode())

But now I'm stuck on how to print the actual string

Leaf Garland · Accepted Answer · 2015-05-15T21:27:33.340

5

If you decorate your ErrorCodes type with the System.Flags attribute then .ToString will format as a list of value names.

[<System.Flags>]
type ErrorCodes = ...

let errors = ErrorCodes.InvalidInputError ||| ErrorCodes.UnknownError

printfn "%O" errors

edited May 15 '15 at 21:27

answered May 14 '15 at 13:01

Leaf Garland

3,647
18
18

score 0 · Answer 2 · answered May 14 '15 at 14:28

If, for whatever reason, you don't want the default flags ToString implementation, you could do something like this:

let inline printFlags (flags: 'e) =
    let ty = typeof<'e>
    (Enum.GetValues ty :?> 'e[], Enum.GetNames ty)
    ||> Array.zip
    |> Seq.filter (fun (v, _) -> v <> enum 0 && flags &&& v = v)
    |> Seq.iter (snd >> printfn "%s")

printFlags (ErrorCodes.InvalidInputError ||| ErrorCodes.UnknownError)

Output:

InvalidInputError
UnknownError

F# HashCode to enum conversion

2 Answers2