相关疑难解决方法(0)

所以我有这个简单的代码，我试图找出 F# 中的类和继承：

type Mkp() =
    abstract tX : unit -> string
    default this.tX() = ""

type A(n : string, v : string) =
    inherit Mkp()
    member this.n = n
    member this.v = v
    override this.tX() = sprintf "%s = \"%s\" " this.n this.v

let test = A "first" "second"
let xxx = "" + test.tX

我收到编译器错误：'string' 类型与'unit -> string' 类型不匹配，但我希望 test.tX 是一个字符串，我做错了什么？