f# - 使用 F# 的可选参数和选项类型

Question

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

虽然 fn1和 fn2工作正常，fn4产生以下错误:

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

MSDN状态:

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，可选参数不会被解释为 F# 选项类型，否则代码会编译。而且我不明白为什么，当我悬停在 ?bo 上时在 fn3工具提示说 val bo: int option但外界只期待 int .我希望有一种不接受任何东西、int、Some int 和 None 的行为。最后一点，我不明白为什么 fn2有效但 fn4才不是。

谢谢澄清

Answer 1

我必须重新考虑正确答案。基于这个问题(和答案):

Propagating optional arguments

看来正确答案如下:

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，答案归功于 desco !