如何从复合泛型类型检索值? [英] How do I retrieve a value from a composite generic type?

问题描述

如何从泛型中检索值?

具体来说，我正在尝试以下操作:

Specifically, I am attempting the following:

// Test
let result = Validate goodInput;;

// How to access record??
let request = getRequest result

代码如下:

type Result<'TSuccess,'TFailure> = 
    | Success of 'TSuccess
    | Failure of 'TFailure

let bind nextFunction lastFunctionResult = 
    match lastFunctionResult with
    | Success input -> nextFunction input
    | Failure f -> Failure f

type Request = {name:string; email:string}

let validate1 input =
   if input.name = "" then Failure "Name must not be blank"
   else Success input

let validate2 input =
   if input.name.Length > 50 then Failure "Name must not be longer than 50 chars"
   else Success input

let validate3 input =
   if input.email = "" then Failure "Email must not be blank"   
   else Success input;;

let Validate = 
    validate1 
    >> bind validate2 
    >> bind validate3;;

// Setup
let goodInput = {name="Alice"; email="[e-mail]"}
let badInput = {name=""; email="[e-mail]"};;

// I have no clue how to do this...
let getRequest = function
    | "Alice", "[e-mail]" -> {name="Scott"; email="[e-mail]"}
    | _ -> {name="none"; email="none"}

// Test
let result = Validate goodInput;;

// How to access record??
let request = getRequest result
printfn "%A" result

推荐答案

您的意思是如何从结果类型中提取记录?通过模式匹配，这就是您在bind中已经完成的工作.

You mean how do you extract the record out of your result type? Through pattern matching, that's what you're already doing in bind.

let getRequest result = 
    match result with
    | Success input -> input 
    | Failure msg -> failwithf "Invalid input: %s" msg

let result = Validate goodInput
let record = getRequest result

这将返回记录或引发异常.由您决定如何处理拥有Result的成功案例和失败案例-可能引发异常，或者将其转换为选项，或者记录消息并返回默认值等.

This will return the record or throw an exception. Up to you how you handle the success and failure cases once you have your Result - that could be throwing an exception, or turning it into option, or logging the message and returning a default etc.

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