创建具有3种不同原始类型的区分联合类型的列表 [英] Create a list of a discriminate union type with 3 different primitive types

问题描述

因此，我尝试创建具有区别的联合类型的列表，例如；

So I am attempting to create a list of a discriminate union type such as;

type ColType = Int of int | Float of float | String of string 

然后插入到列表中，例如

And then insert into a list, such as

let addToList (list : ColType list) (col : ColType) =
let list' = list @[col]
list'

但是我不确定如何初始化coltype值，因为我只能获取int-> coltype等值.

However I am unsure how to initialize the coltype values as I only get values such as int -> coltype etc.

我尝试了此功能

let createColType x = 
    if x.GetType() = int then  
        Int x
    else if x.GetType() = float then 
        Float x 
    else if x.GetType() = string then  
        String x
    else 
        String x

显然哪个都不行，因为它将返回不同的值，那么您将如何解决呢?

Which obviously doesnt work as it will return different values, so how would you go about solving this?

推荐答案

使用match检查多个选项，并使用:?匹配类型:

Use match to check multiple options and :? to match the type:

let createColType x = 
    match box x with
    | :? int    as i -> ColType.I i
    | :? float  as f -> ColType.F f
    | :? string as s -> ColType.S s
    |_-> failwithf "Type not supported %A" <| x.GetType().FullName

createColType  1  |> printfn "%A" // shows:  I 1
createColType  2. |> printfn "%A" // shows:  F 2.0
createColType "3" |> printfn "%A" // shows:  S "3"

这篇关于创建具有3种不同原始类型的区分联合类型的列表的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！