所以我试图创建一个歧视联合类型的列表,如;
type ColType = Int of int | Float of float | String of string
然后插入到列表中,例如
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,因为我只获取int - > coltype等值。
我试过这个功能
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
这显然不起作用,因为它将返回不同的值,所以你将如何解决这个问题?
使用match
检查多个选项和:?
以匹配类型:
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"
type Food = Hamburgers of int | Soda of float | Other of string
module Food =
let tryCreate food =
match box food with
| :? int as i -> Some(Hamburgers i)
| :? float as f -> Some(Soda f)
| :? string as s -> Some(Other s)
| _ -> None
let burgers = Hamburgers 7
let soda = Soda 3.2
let mozzarellaSticks = Other "Mozzarella Sticks"
let mysteryMeat = Option.toList(Food.tryCreate "nobody knows")
let list = [burgers; soda; mozzarellaSticks] @ mysteryMeat
通过使用Option
作为我的tryCreate
的返回类型,我不会得到任何运行时异常。您还会注意到我已经尝试创建与我的业务目标相关联的DU标签。这使得表达意图更容易,并使联合比简单的整数,字符串和浮点数更有用。大多数时候我知道我的类型,因为类型对应于业务用途,所以我不必编写或使用tryCreate。通常在实践中,将基元映射到我们有区别的联盟并不是很有意义,例如,如果我们添加了一个| Hotdogs of int
,如果我们添加的任何int是热狗或汉堡包,则它是不明确的。