如何在 F# 中实例化类及其属性

Question

遵循代码 C#：

var body = new CustomerRequest
{
    Method = "CREDIT_CARD",
    CreditCard = new Creditcard
    {
        ExpirationMonth = "06",
        ExpirationYear = "2022",
        Number = "4012001037141112",
        Cvc = "123"
    }
};

我是 F# 的新手，我不能像 C# 那样实例化类，请参阅下面的 F# 代码：

let body = CustomerRequest
(
    Method = "CREDIT_CARD"     // Help here
)

我无法将 C# 转换为 F#

Answer 1

如果您使用的是惯用的 F#，您可以使用 Records instead of classes 来建模。

你可以这样做：

type CreditCard = {
    ExpirationMonth: int;
    //More
}

type CustomerRequest = {
    Method: string;
    CreditCard: CreditCard;
}

let req = {
    Method = "Credit"
    CreditCard = {
        ExpirationMonth = 6
        //More
    }
}

编译器有类型推断，这意味着它可以根据你在其中的字段猜测 req 是一个 CustomerRequest，CreditCard 也是如此 - 你可以如果确实需要，请提示类型。

如果您真的想要类 - 也许您必须与 C# 代码互操作，那么您可以这样做：

type CreditCard2(expirationMonth:int) = 
    member this.ExpirationMonth = expirationMonth

type CustomerRequest2(method: string, creditCard: CreditCard2) = 
    member this.Method = method
    member this.CreditCard = creditCard

let req2 = CustomerRequest2 ("Credit", CreditCard2 (5))

Answer 2

我想这就是您要找的：

CreditCard.fs

namespace Whosebug

type CreditCard() =
    member val ExpirationDate = "" with get, set
    member val ExpirationYear = "" with get, set
    member val Number = "" with get, set
    member val Cvc = "" with get, set

type CustomerRequest() =
    member val Method = "" with get, set
    member val CreditCard = new CreditCard() with get, set

Program.fs

open System
open Whosebug

[<EntryPoint>]
let main argv =
    let body = new CustomerRequest(Method = "CREDIT_CARD",
                                        CreditCard = CreditCard(
                                            ExpirationDate = "06",
                                            ExpirationYear = "2022",
                                            Number = "4012001037141112",
                                            Cvc = "123"
                                        ))
    0

我对 F# 了解不多，所以也许像 David Shaw 使用的那样使用 Records 是更明智的设计。但基本上这会让你在没有参数构造函数和类型中没有可变的非属性值的情况下做到这一点。

Answer 3

如果您只想使用 named arguments 来设置您正在构建的类的属性：语法与 C# 非常相似。至于缩进的层级，需要和第一个参数对齐。

let body =
    CustomerRequest(
        Method = "CREDIT_CARD",
        CreditCard =
            Creditcard(
                ExpirationMonth = "06",
                ExpirationYear = "2022",
                Number = "4012001037141112",
                Cvc = "123" ) )

如何在 F# 中实例化类及其属性

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如何在 F# 中实例化 类 及其属性

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如何在 F# 中实例化类及其属性