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Question about multiple constructors (beginner)
f#

I have this simple class:

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type MyClass(bytes) = 

  let hexString = ByteToString bytes

  [ OverloadID("2")>]

  new (hexStr) =

      let bytes = StringToByte hexStr

      new MsgContainer(bytes)

  member this.Bytes = bytes

  member this.HexString = hexString

It's purpose is to take one argument (byte[] or string) and convert it to another type (byte[] -> string or vice versa)

This thing works, but I really don't like overloaded constructor because it converts string to byte[] and then calls original constructor that again converts byte[] to string.

How could this be written?

I would not want to use explicit syntax, since members in this class are immutable.

Can this be written with optional arguments? In that case, there should be some filter that forbids using two arguments in constructor.

p.s. Is there any guide how o format code on this forum? It ate spaces on beginning of the line and I could not escape "<" and ">" in [<OverloadID("2")> ] . I checked everything, I tried BBCode, but nothing worked.

.

Hi zendar,

I'd probably use a Choice type here. A Choice type is a discriminated union type which allows you to choose between 2 (or more) values:

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let ByteToString (x:Byte) = Convert.ToString(x)

let StringToByte (x:string) = Convert.ToByte(x)

type MyClass(bytesOrString) = 

    let (hexString, bytes) = 

        match bytesOrString with

        | Choice2_1 bytes -> (ByteToString bytes, bytes)

        | Choice2_2 hexString -> (hexString, StringToByte hexString) 

    member this.Bytes = bytes

    member this.HexString = hexString

//instantiate MyClass

let strInstance = new MyClass(Choice2_2 "a string")

This may not be exactly what you want (I was to lazy to do conversion from string to byte[]...), but it should show the general idea.

BTW, as you can see I have the same problem using formatting as you have. I think though, it has something to do with the browser you use as well...I've had better results using IE.

hope this helps.

By on 12/29/2008 7:59 AM ()

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