复制工会案例但在F#中使用不同的值

Question

在F#中,我想基于现有实例构造一个区分联合的实例(正确的术语？).例:

type union Currency =
    | Dollar of int
    | Euro of int

let lowPrice = Dollar 100 (* or, it could be *) let lowPrice = Euro 100
let highPrice = (* of the same union case as lowPrice but with value 200 *)

我可以插入什么代码来代替注释来创建该效果？

Answer 1

你可以做到

let highPrice =
    let n = 200
    match lowPrice with
    | Dollar _ -> Dollar n
    | Euro _ -> Euro n

但计量单位可能更好.

编辑

或者,也许你想要

type MoneyType = Dollar | Euro
type Currency = Currency of MoneyType * int
let lowPrice = Currency(Dollar, 100)
let highPrice = 
    match lowPrice with
    | Currency(kind, _) -> Currency(kind, 200)