Question

type SQLConn =
    val mutable private connection  : string option

    member this.Connection
        with get() : string   = this.connection.Value
        and  set(v)           = this.connection           <- Some v

    new (connection : string) = {connection = Some connection;}
    new() = SQLConn @"Data Source=D:\Projects\AL\Service\ncFlow\dbase\dbflow.db3; Version=3;Password=432432434324"

I want to use “let x = 5+5” there or something like that, so how can I use private functions in my type (class) (record) , I know that I can use them if I do SQLConn() , but then I can’t use val, I want to use both : val and let …

thank you

Answer 1

As Tim explains, you can only use local let bindings with the implicit constructor syntax. I would definitely follow this approach as it makes F# code more readable.

Do you have any particular reason why you also want to use val in your code? You can still use them with the implicit constructor syntax, but they have to be mutable and initialized using mutation:

type SQLConn(connection:string) as x = 
  let mutable connection = connection

  // Declare field using 'val' declaration (has to be mutable)
  [<DefaultValue>]
  val mutable a : int 

  // Initialize the value imperatively in constructor
  do x.a <- 10

  member this.Connection 
    with get() = connection and set(v) = connection <- v 

  new() = SQLConn @"Data Source=.." 

As far as I can tell val is only needed to create fields that are not private (which may be required by some code-gen based tools like ASP.NET, but is otherwise not really useful).