使用F#的可选参数和选项类型 [英] Optional parameters and option types using F#

问题描述

考虑以下代码:

type Test () =
  member o.fn1 (?bo) = 1
  member o.fn2 (?bo) = o.fn1 bo

  member o.fn3 (?bo) = 1 + bo.Value
  member o.fn4 (?bo) = o.fn3 bo

fn1和fn2正常工作时，fn4会产生以下错误:

While fn1 and fn2 work just fine, fn4 produces the following error:

init.fsx(6,30):错误FS0001:该表达式应具有int类型，但此处具有类型'a option

init.fsx(6,30): error FS0001: This expression was expected to have type int but here has type 'a option

MSDN 状态:

可选参数被解释为F#选项类型，因此您可以使用带有Some和None的匹配表达式，以常规方式查询选项类型.

Optional parameters are interpreted as the F# option type, so you can query them in the regular way that option types are queried, by using a match expression with Some and None.

对我来说，可选参数不会解释为F#选项类型，否则代码将被编译.此外，我不明白为什么，当我将鼠标悬停在fn3中的?bo上时，工具提示显示val bo: int option，但从外面只能看到int.我期望一种不接受任何内容的行为，即int，Some int和None.最后一点，我不明白为什么fn2起作用但fn4不能起作用.

To me, optional parameters are not interpreted as the F# option type otherwise the code would compile. Moreover I do not understand why, when I hover over ?bo in fn3 the tooltip says val bo: int option but from outside expects only int. I would expect a behavior of accepting nothing, int, Some int and None. And as the last note, I do not understand why fn2 works but fn4 does not.

感谢您的澄清

推荐答案

我必须重新考虑正确的答案.基于这个问题(和答案):

I have to reconsider the correct answer. Based on this question (and answer):

传播可选参数

它接缝正确的答案如下:

it seams that the correct answer is the following:

type Test () =
  member o.fn1 (?bo) = 1
  member o.fn2 (?bo) = o.fn1 bo

  member o.fn3 (?bo) = 1 + bo.Value
  member o.fn4 (?bo) = o.fn3 (?bo = bo)

这是一个简洁的功能，您可以在 desco 上找到答案.

It is a neat feature and credits for the answer go to desco!

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