Question

F＃有许多不同的方法来定义类型中的变量/成员。我应该何时在F＃中使用let，member val和member this.，它们之间有什么区别？静态和可变成员怎么样？

Answer 1

我发现更容易反编译正在发生的事情，所以：

type Region() =
  let mutable t = 0.0f
  member val Width = 0.0f
  member x.Height = 0.0f
  member val Left = 0.0f with get,set
  member x.Top with get() = 0.0f and set(value) = t <- value

实际上如下：

public class Region
{
    internal float t;

    internal float Width@;

    internal float Left@;

    public float Width
    {
        get
        {
            return this.Width@;
        }
    }

    public float Height
    {
        get
        {
            return 0f;
        }
    }

    public float Left
    {
        get
        {
            return this.Left@;
        }
        set
        {
            this.Left@ = value;
        }
    }

    public float Top
    {
        get
        {
            return 0f;
        }
        set
        {
            this.t = value;
        }
    }

    public Region() : this()
    {
        this.t = 0f;
        this.Width@ = 0f;
        this.Left@ = 0f;
    }
}

Answer 2

此示例解释了语法之间的区别：

type MyClass() =
    let random  = new System.Random() 
    [<DefaultValue>] val mutable field : int
    member val AutoProperty = random.Next() with get, set
    member this.ExplicitProperty = random.Next()

let c = new MyClass()
// class1.random is not accessible
c.field <- 42 // 'field' is accessible

// An automatic property is only evaluated upon initialization, and not every time the property is accessed
printfn "AutoProperty = %d" c.AutoProperty // x
printfn "AutoProperty = %d" c.AutoProperty // Still x

// The value of the explicit property is evaluated each time
printfn "ExplicitProperty = %d" c.ExplicitProperty // y
printfn "ExplicitProperty = %d" c.ExplicitProperty // The value is re-evaluated so you'll get a different value

我什么时候应该使用let，member val和member。

2 个答案: