F#中的C#对象初始化语法

Question

请注意:这个问题和这个问题不一样.

我最近遇到了一些我以前没有遇到过的C#语法:

在F#中有没有办法做到这一点？

class Two
{
    public string Test { get; set; }
}

class One
{
    public One()
    {
        TwoProperty = new Two();
    }
    public Two TwoProperty { get; private set; }
}

var test = new One(){ TwoProperty = { Test = "Test String" }};

(注意TwoProperty当setter是私有时初始化器中的初始化 - 它是在存储的对象上设置属性TwoProperty,但不在Two属性中存储新实例)

编辑:我最近在monotouch的构造函数中遇到了一些C#代码,如下所示:

nameLabel = new UILabel {
    TextColor = UIColor.White,
    Layer = {
        ShadowRadius = 3,
        ShadowColor = UIColor.Black.CGColor,
        ShadowOffset = new System.Drawing.SizeF(0,1f),
        ShadowOpacity = .5f
    }
};

我能想出的最好的F#翻译是这样的:

let nameLabel = new UILabel ( TextColor = UIColor.White )
do let layer = nameLabel.Layer
   layer.ShadowRadius <- 3.0f
   layer.ShadowColor <- UIColor.Black.CGColor
   layer.ShadowOffset <- new System.Drawing.SizeF(0.0f,1.0f)
   layer.ShadowOpacity <- 0.5f  

这并不可怕,但它确实有更多的噪音与重复的layer参考加上更多的命令和更少的声明.

Answer 1

我不认为F#允许在初始化期间设置嵌套属性.假设您是API的作者,解决方法是将整个对象传递给构造函数.这消除了对具有不同可访问性的getter和setter的需求,并使整个F#代码更加清晰.

type Two() =
    member val Test = "" with get, set

type One(twoProperty) =
    member val TwoProperty = twoProperty

let test = One(Two(Test="foo"))

正如您在评论中提到的,您可以创建一个辅助函数,接受各种属性作为可选参数.类型扩展适用于此:

type UILayer with
    member this.Configure(?shadowRadius, ?shadowColor, ?shadowOffset, ?shadowOpacity) = 
        this.ShadowRadius <- defaultArg shadowRadius this.ShadowRadius
        this.ShadowColor <- defaultArg shadowColor this.ShadowColor
        this.ShadowOffset <- defaultArg shadowOffset this.ShadowOffset
        this.ShadowOpacity <- defaultArg shadowOpacity this.ShadowOpacity

let nameLabel = UILabel(TextColor=UIColor.White)
nameLabel.Layer.Configure(
    shadowRadius=3.0f, 
    shadowColor=UIColor.Black.CGColor, 
    shadowOffset=SizeF(0.0f, 1.0f), 
    shadowOpacity=0.5f)

Answer 2

将构造封装到单独的初始化函数中是否有意义？

let layerInit layer radius color offset opacity =
    do
       layer.ShadowRadius <- radius
       layer.ShadowColor <- color
       layer.ShadowOffset <- offset
       layer.ShadowOpacity <- opacity
    layer // I do this in case you want to use this fluently or pass in new Layer()

然后在您的代码中使用它：

let nameLabel = new UILabel ( TextColor = UIColor.White )
layerInit nameLabel.Layer 3.0f UIColor.Black.CGColor new System.Drawing.SizeF(0.0f,1.0f) 0.5f |> ignore