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Allow optional members to be inferred as part of signature when appropriate #745

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Happypig375 opened this issue Jun 8, 2019 · 0 comments

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commented Jun 8, 2019

Allow optional members to be inferred as part of signature when appropriate

I propose we allow optional members to be inferred as part of inferred signature for member calls.

The existing way of approaching this problem in F# is writing wrapper functions.

type C() = static member M x = ()
let x = 1 |> C.M //ok
type C() = static member M ?x = ()
let x = 1 |> C.M //proposed to allow, currently error FS0001: This expression was expected to have type 'int' but here has type 'unit'    
type C() = static member M ?x = ()
let x = 1 |> (fun x -> C.M x) //ok, but ugly workaround
type C() = static member M (x : int, ?y : int) = printfn "%A, %A" x y
C.M 1 //prints "1, <null>"
1 |> C.M //prints "1, <null>"
C.M(1, 2) //prints "1, Some 2"
(1, 2) |> C.M //error currently, will print "1, Some 2"

The current proposal will provide no way to specify ?x = Some 1 like in member calling.

Pros and Cons

The advantages of making this adjustment to F# are

  1. reduced boilerplate
  2. better uniformity between member calling and pipelining
  3. reduce surprises when trying to pipeline

The disadvantage of making this adjustment to F# is added complexity.

Extra information

Estimated cost (XS, S, M, L, XL, XXL): S~M

Related suggestions: Nope

Affidavit (please submit!)

Please tick this by placing a cross in the box:

  • This is not a question (e.g. like one you might ask on stackoverflow) and I have searched stackoverflow for discussions of this issue
  • I have searched both open and closed suggestions on this site and believe this is not a duplicate
  • This is not something which has obviously "already been decided" in previous versions of F#. If you're questioning a fundamental design decision that has obviously already been taken (e.g. "Make F# untyped") then please don't submit it.

Please tick all that apply:

  • This is not a breaking change to the F# language design
  • I or my company would be willing to help implement and/or test this
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