F# 嵌套记录

Question

嵌套记录

记录是否类似于字典，它是一棵具有名称的对象树？或者记录只是简单类型的列表

let r = { b = { a = 2 } } // is this possible? if not, how to achieve? is this useful in f#?

对于我来说，有歧视的工会可以实现类似的行为（下面的代码）


// Discriminated union for a card's suit 

type Suit = | Heart | Diamond | Spade | Club 
let suits = [Heart; Diamond; Spade; Club]
suits

// Discriminated union for playing cards

type PlayingCard = 
    | Ace of Suit 
    | King of Suit 
    | Queen of Suit
    | Jack of Suit 
    | ValueCard of int * Suit

// generating a deck of cards

let deckOfCards = 
    [
        for suit in [Spade; Club; Heart; Diamond] do   
            yield Ace(suit)
            yield King(suit)
            yield Queen(suit)
            yield Jack(suit)
            for value in 2..10 do
                yield ValueCard(value, suit)
    ]

它有点类似于 python 或 idk 中的字典。下面的代码是虚拟的


type Customer = 
    {
        FirstName : string
        Contacts = 
            {
                WorkPhone : string
                MobilePhone : string
            }
        
    }

Answer 1

可以使用 anonymous records:

创建嵌套类型

type Customer = 
    {
        FirstName : string
        Contacts :
            {|
                WorkPhone : string
                MobilePhone : string
            |}
    }

let customer =
    {
        FirstName = "John"
        Contacts =
            {|
                WorkPhone = "123-456-7890"
                MobilePhone = "234-567-8901"
            |}
    }

Answer 2

是的，您可以有嵌套记录，但就像在您的示例中使用可区分联合一样，您需要为嵌套类型命名：

type CustomerConracts =
    {
        WorkPhone : string
        MobilePhone : string
    }

type Customer = 
    {
        FirstName : string
        Contacts: CustomerConracts       
    }

let c = { FirstName = "John", Contacts = { WorkPhone = "123", Mobile phone = "098" } }

Answer 3

您可以在代码中看到一些模式，但记录与字典不相似。您可以将它们视为类而具有强类型 public 属性。如果需要创建字典，则必须使用可用的 map/dictionary 类之一或实现自己的字典。例如，看一下 Map 类型。 https://fsharp.github.io/fsharp-core-docs/reference/fsharp-collections-fsharpmap-2.html

type Contact = 
    {
        WorkPhone : string
        MobilePhone : string
    }

type Customer = 
    {
        FirstName : string
        Contacts : Contact
    }


let cust : Customer = 
    { 
      FirstName = "Joe"
      Contacts = { WorkPhone="1800131313"; MobilePhone="0863331311" } 
    }

上面的代码表明您可以嵌套记录类型。除了按照@brianberns 的建议使用匿名记录外，您还可以声明您计划嵌套的数据类型。

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