可变变量“i"的使用方式无效.? [英] The mutable variable 'i' is used in an invalid way.?

问题描述

我正在尝试用 F# 编写一些简单的代码，但出现此错误:

I am attempting to write some simple code in F#, and i get this error:

Error   1   The mutable variable 'i' is used in an invalid way. Mutable variables may not be captured by closures. Consider eliminating this use of mutation or using a heap-allocated mutable reference cell via 'ref' and '!' 

代码:

let printProcess = async {
        let mutable i = 1;
        while true do
            System.Console.WriteLine(i);//error is here
            i <- i + 1;
    }

为什么它不让我打印变量?

Why won't it let me print the variable?

推荐答案

您不能在闭包中引用可变变量，其中包括 seq{} 和 async{} 块等结构.

You can't refer to mutables inside a closure, and that includes such constructs as seq{} and async{} blocks.

你可以写

let printProcess = async {
        let i = ref 1
        while true do
            System.Console.WriteLine(!i)
            i := !i + 1
    }

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