如何做F＃记录的参数验证 [英] How to do argument validation of F# records

问题描述

F＃可以轻松定义类型，例如

F# makes it easy to define types such as

type coords = { X : float; Y : float }

但是如何为构造函数定义约束/详细类定义语法？例如。如果我想要协调从（0,0）开始或抛出异常。

but how do I define constraints/check arguments for the constructor without going into the more verbose class definition syntax? E.g. if I want coords to start from (0,0) or throw an exception.

此外，如果我将我的定义更改为类，我需要实现Equals 。所有的锅炉板代码我不想（和我在C＃中，我试图逃避）。

Moreover, if I change my definition to a class I need to implement Equals() etc. all the boiler plate code I don't want (and which I have in C# that I'm trying to get away from).

推荐答案

您可以将实现设为私有。你仍然得到结构上的平等，但是你失去了直接的字段访问和模式匹配。您可以使用有效模式恢复该功能。

You can make the implementation private. You still get structural equality but you lose direct field access and pattern matching. You can restore that ability using active patterns.

//file1.fs

type Coords = 
  private { 
    X: float
    Y: float 
  }

[<CompilationRepresentation(CompilationRepresentationFlags.ModuleSuffix)>]
module Coords =
  ///The ONLY way to create Coords
  let create x y =
    check x
    check y
    {X=x; Y=y}

  let (|Coords|) {X=x; Y=y} = (x, y)

//file2.fs

open Coords
let coords = create 1.0 1.0
let (Coords(x, y)) = coords
printfn "%f, %f" x y

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