F# 类型类持久计数器

Question

绅士们，

过去的程序/确定性程序员与 F# 函数式斗争......

我需要一些计数器来记录程序各个区域的计数。以下代码编译干净并且似乎可以工作，但“ctr”永远不会增加。

任何帮助表示赞赏，伊恩

type Count() as this = 
    let mutable ctr = 0
    do
        printfn "Count:Constructor: %A" ctr
    member this.upctr : int = 
        let ctr  = ctr + 1 
        printfn "inCount.upctr %d" ctr
        ctr

let myCount = new Count()
printfn "MyCtr1 %d" (myCount.upctr)
let fred = myCount.upctr
let fred = myCount.upctr

Answer 1

该值ctr是可变的。使用：

ctr  <- ctr + 1  // this will mutate the value contained in ctr

代替

// this will create a new binding which is not mutable
// and will shadow the original ctr
let ctr = ctr + 1  

另请注意警告，它告诉您不需要 as this在类型声明中。