f# - F# 中的单例区分联合，类型和标签的名称相同

Question

我在 F# 文件中有以下代码:

module ORDERS

type OrderId =           // TypeName
    | OrderId of string  // LabelName: same as TypeName!
    with 
    static member getValue (OrderId orderId) =
        orderId

在另一个文件中，我可以使用这样的函数:

// This code works.
module Application
open ORDERS

let x = OrderId "1111"
let extractedValue = 
    x 
    |> OrderId.getValue

但是，如果我尝试删除“打开的订单”并用它们的完整路径替换代码，我会收到错误消息:

// This code fails.
module Application

// This is OK
let x2 = ORDERS.OrderId "11111"

// This has error!
let extractValue2 = 
    x2
    |> ORDERS.OrderId.getValue

我认为原因是在第二个代码中，F# 无法区分 TypeName "OrderId"和 LabelName "OrderId"

问题:

1. 为什么删除“open ORDERS”，但指定完整路径会导致代码失败？这两个代码(带“open ORDERS”；不带“open ORDERS”但指定函数全名)不是等价的吗？

---

附加问题:

1. 将 TypeName 和 LabelName 重命名为不同的名称以便它们不会相互冲突会更好吗？例如

   module ORDERS
   type OrderIdType =            // TypeName
       | OrderIdLabel of string  // LabelName: different from TypeName!
       with 
       static member getValue (OrderIdLabel orderId) =
           orderId
   

非常感谢。

Answer 1

您可以通过将静态方法替换为模块级 getOrderIdValue 函数来实现如下所示的工作:

module ORDERS =

    type OrderId =           // TypeName
        | OrderId of string  // LabelName: same as TypeName!
        with 
        static member getValue (OrderId orderId) =
            orderId

    let getOrderIdValue (OrderId orderId) =
            orderId

module Application =
    open ORDERS

    let x = OrderId "1111"
    let extractedValue = 
        x 
        |> OrderId.getValue

module ApplicationWithoutOpenOrders =

    // This is OK
    let x2 = ORDERS.OrderId "11111"

    // This has error!
    let extractValue2 = 
        x2
        |> ORDERS.getOrderIdValue