单例在F＃中区分了Union，类型和标签的名称相同

Question

I have the following code in an F# file:

module ORDERS

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

and in another file, I can utilize the function like this:

// This code works.
module Application
open ORDERS

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

However, if I try to remove the "open ORDERS" and replace the code with their full path, I get an error:

// This code fails.
module Application

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

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

I believe the reason is that in the second code, F# cannot differentiate the TypeName "OrderId", and the LabelName "OrderId"

Question:

1. Why does removing "open ORDERS", but specifying the full path will cause the code to fail? Aren't the two codes (with "open ORDERS"; without "open ORDERS" but specify full name of functions) equivalent?

---

Additional question:

2. Would it be better to rename the TypeName and LabelName differently so that they won't conflict with each other? eg

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

Thank you very much.

Answer 1

You could make this work as shown below by replacing the static method with a module-level getOrderIdValue function instead:

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