Adding StructLayout attribute to F# type with implicit constructor

.net, f#, structlayout

Solution

As the error message said, `StructLayout` should work with explicit constructors:

type Package =
    abstract member Date : int
    abstract member Save : unit -> unit

[<type:StructLayout(LayoutKind.Sequential, Pack=1, CharSet=CharSet.Ansi)>]
type Instant =
    val mutable Date: int
    val mutable Value: int
    new(date, value) = {Date = date; Value = value}

    interface Package with
        member x.Date = x.Date
        member x.Save() = x.Value |> ignore

If you have any further problem with `FieldOffset`, please take a look at code examples here.

Problem

I've got: ``` type Package = abstract member Date : int abstract member Save : unit -> unit [<type:StructLayout(LayoutKind.Sequential, Pack=1, CharSet=CharSet.Ansi)>] type Instant(date : int, value : int) = let mutable _date = date let mutable _value = value member X.Value : int = _value interface Package with member X.Date : int = _date member X.Save() = ... ``` but getting error: Only structs and classes without implicit constructors may be given the 'StructLayout' attribute so I realize it must be something alike: ``` type Instant = struct val Date : byte array ... ``` But this way I lost my interface. In C# for example adding `type:StructLayout` is possible for this type of classes (I think). How must I refactor my code to avoid this error?

Original source