如何从F#向C#返回空元组? [英] How do you return a null Tuple from f# to c#?

问题描述

我具有此类型正确的C#函数:

I have this type-correct C# function:

static System.Tuple<int,int> f(int n) { 
  switch (n) { 
    case 0: return null;
    default: return System.Tuple.Create(n,n+1);
  }
}

我尝试在F#中重新实现它:

I try to re-implement it in F#:

let f = function 
| 0 -> null 
| n -> System.Tuple.Create(n, n+1)

类型检查器不同意，

error FS0001: The type '('a * 'b)' does not have 'null' as a proper value.

如何在F#中重新实现原始的C#函数 f ?

How do I re-implement the original C# function f in F#?

请注意，虽然这看起来像是如何在F#中返回null"(答案:不要，使用Option)的问题，但我们在询问如何从C#消费者从F#返回"中稍有不同."(不能使用Option，下面提供有用的答案).

Note that while this looks like the question "how do I return null in F#" (answer: don’t, use Option) we are asking the slightly different "how do we return null from F# for C# consumers" (can’t use Option, helpful answer below).

推荐答案

如果需要它与C#互操作，则可以使用 Unchecked.Defaultof 像这样:

If you need it to interop with C#, you can use Unchecked.Defaultof like so:

let f = function
    | 0 -> Unchecked.Defaultof<_>
    | n -> (n, n + 1)

但是，在F#中强烈建议不要使用空值，并且如果互操作性不是您的主要关注点，那么使用选项会更加自然:

However, using null values is strongly discouraged in F#, and if interoperability is not your main concern, using an option is much more natural:

let f = function
    | 0 -> None
    | n -> Some (n, n + 1)

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