此 Result<'T,'TFailure> 类型允许你编写可撰写的错误容错代码。
语法
// The definition of Result in FSharp.Core
[<StructuralEquality; StructuralComparison>]
[<CompiledName("FSharpResult`2")>]
[<Struct>]
type Result<'T,'TError> =
| Ok of ResultValue:'T
| Error of ErrorValue:'TError
注解
Result有关内置组合器的模块，请参阅该Result模块。 类型。
请注意，结果类型是一个 结构区分联合。 结构相等语义在此处适用。
该 Result 类型通常用于单一错误处理中，这通常称为 F# 社区内 面向铁路的编程 。 以下简单示例演示了此方法。
// Define a simple type which has fields that can be validated
type Request =
{ Name: string
Email: string }
// Define some logic for what defines a valid name.
//
// Generates a Result which is an Ok if the name validates;
// otherwise, it generates a Result which is an Error.
let validateName req =
match req.Name with
| null -> Error "No name found."
| "" -> Error "Name is empty."
| "bananas" -> Error "Bananas is not a name."
| _ -> Ok req
// Similarly, define some email validation logic.
let validateEmail req =
match req.Email with
| null -> Error "No email found."
| "" -> Error "Email is empty."
| s when s.EndsWith("bananas.com") -> Error "No email from bananas.com is allowed."
| _ -> Ok req
let validateRequest reqResult =
reqResult
|> Result.bind validateName
|> Result.bind validateEmail
let test() =
// Now, create a Request and pattern match on the result.
let req1 = { Name = "Phillip"; Email = "phillip@contoso.biz" }
let res1 = validateRequest (Ok req1)
match res1 with
| Ok req -> printfn $"My request was valid! Name: {req.Name} Email {req.Email}"
| Error e -> printfn $"Error: {e}"
// Prints: "My request was valid! Name: Phillip Email: phillip@consoto.biz"
let req2 = { Name = "Phillip"; Email = "phillip@bananas.com" }
let res2 = validateRequest (Ok req2)
match res2 with
| Ok req -> printfn $"My request was valid! Name: {req.Name} Email {req.Email}"
| Error e -> printfn $"Error: {e}"
// Prints: "Error: No email from bananas.com is allowed."
test()
正如你所看到的，如果强制所有验证函数返回一个，则很容易将各种验证函数链接在一 Result起。 这样，你可以将类似功能分解成小块，这些小块与你需要它们一样可组合。 这也具有在一轮验证结束时 强制 使用 模式匹配 的附加价值，从而强制实施更高程度的程序正确性。
