F#中的DependencyAttribute类

Question

我正在使用Petzold使用Xamarin Forms创建移动应用程序书,将C#代码翻译成F#,其中F#代码在GitHub上不可用(他在第7章后停止发布FS).在第9章,第189页中,他使用了Dependency属性,如下所示:

[assembly: Dependency(typeof(DisplayPlatformInfo.iOS.PlatformInfo))]
namespace DisplayPlatformInfo.iOS
{
  public interface IPlatformInfo
 {
 string GetModel();
 string GetVersion();
 }
  using System;
 using UIKit;
 using Xamarin.Forms;
  public class PlatformInfo : IPlatformInfo
 {
 UIDevice device = new UIDevice();
 //etc...

我想在F#中做相同的事情.我创建了类型,并且我可以添加该属性的唯一位置是通用的do()语句:

type PlatformInfo () =
    [<assembly: Dependency(typeof(Greetings.iOS.PlatformInfo))>]
    do()

    interface IPlatformInfo with
        member this.GetModel () = 
            let device = new UIDevice()
            device.Model.ToString()
        member this.GetVersion () = 
            let device = new UIDevice()
            String.Format("{0} {1}", device.SystemName, device.SystemVersion)

问题是我得到了

警告:此构造中将忽略属性.

我该如何将此属性放入类型中？

Answer 1

F#中的程序集级别属性需要是顶层的模块.

我将上面的C#翻译为:

namespace rec DisplayPlatformInfo.iOS

// Make a module specifically for this attribute
module DisplayPlatformAssemblyInfo =
    [<assembly: Dependency(typeof(Greetings.iOS.PlatformInfo))>]
    do ()

type IPlatformInfo =
    abstract member GetModel : unit -> string
    abstract member GetVersion : unit -> string

// ... Implement your type, etc