F#类型测试模式匹配:分解元组对象

问题描述

很好奇为什么我不能这样做:

Just curious why I can't do this:

let myFn (data : obj) =
    match data with
    | :? (string * string) as (s1, s2) -> sprintf "(%s, %s)" s1 s2 |> Some
    | :? (string * string * int) as (s1, s2, i) -> sprintf "(%s, %s, %d)" s1 s2 i |> Some
    | _ -> None

怎么来?

推荐答案

请参见 F#规范，第7.3节作为模式"

See F# spec, section 7.3 "As patterns"

as模式的格式为 pat as ident

这意味着您需要在 as 之后使用标识符:

Which means you need to use an identifier after as:

let myFn (data : obj) =
    match data with
    | :? (string * string)       as s1s2  -> let (s1, s2)    = s1s2  in sprintf "(%s, %s)" s1 s2 |> Some
    | :? (string * string * int) as s1s2i -> let (s1, s2, i) = s1s2i in sprintf "(%s, %s, %i)" s1 s2 i |> Some
    | _ -> None

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