f＃类构造函数格式

Question

I am creating a program that takes an email and converts it into json. In the interest of learning functional languages I thought it would be a good opportunity to learn F#. So first off I want a message class that can then easily be serialized into json. This class will have some members that can be null. Because of these optional parameters I am using the following format

type Email(from:string, recipient:string, ?cc:string .........) =
    member x.From = from
    member x.Recipient = recipient.....

This class actually has a lot of members as I want to store every piece of information that an email could have. What happens is if I try to format the constructor myself by splitting it onto multiple lines I get warnings. How do people make such a gigantic constructor look good in f#? Is there a better way to do this?

On a similar note, I'm not finding visual studio very helpful for f#, what are other people using to code? I think there is a mode for emacs for example...

Answer 1

There should not be any warnings if all "newlined" parameters start at the same column. For example:

type Email(from:string, recipient:string,
           ?cc:string) =
    member x.From = from
    member x.Recipient = recipient

(I personally enjoy using Visual Studio for F#. I doubt there is an IDE with more complete support.)

Answer 2

As an alternative to creating constructor that takes all properties as parameters, you can also create an object with mutable properties and then specify only those that you want to set in the construction:

type Email(from:string, recipient:string) =
  member val From = from with get, set
  member val Recipient = recipient with get, set
  member val Cc = "" with get, set
  member val Bcc = "" with get, set

let eml = Email("me@me.com", "you@you.com", Cc="she@she.net")

This is using a new member val feature of F# 3.0. Writing the same in F# 2.0 would be pretty annoying, because you'd have to define getter and setter by hand.