F# - 模式匹配区分联合和访问对象的属性

Question

来自 F# tour 我有这个例子

type Person = {
    First : string
    Last  : string
 }

/// A Discriminated Union of 3 different kinds of employees
type Employee =
    | Engineer of engineer: Person
    | Manager of manager: Person * reports: List<Employee>
    | Executive of executive: Person * reports: List<Employee> * assistant: Employee

let rec findDaveWithOpenPosition(emps: List<Employee>) = 
    emps
    |> List.filter(function 
                    | Manager({First =  "Dave"}, []) -> true
                    | Executive({First = "Dave"}, [], _) -> true
                    | _ -> false
                    )

但是我想在匹配对象后访问对象，如下所示：

let rec findDaveWithOpenPos2(emps: List<Employee>) =
    List.filter (fun (e:Employee) ->
                    match e with
                        | Manager({First = "Dave"}, []) -> e.Last.Contains("X") //Does not compile
                        | Executive({First = "Dave"}, [], _) -> true
                        | _ -> false
                    ) emps

所以我想在右侧静态键入“e”作为 Person 或 Employee 或 Manager 变量，并可以访问它的属性。 可能吗？有没有更好的结构？

Answer 1

您可以使用as 在Manager 案例中命名Person 实例：

let rec findDaveWithOpenPos2(emps: Employee list) =
    List.filter (fun (e:Employee) ->
                    match e with
                        | Manager({First = "Dave"} as p, []) -> p.Last.Contains("X")
                        | Executive({First = "Dave"}, [], _) -> true
                        | _ -> false
                    ) emps