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Allow tupled returns and outrefs in functions outputs #787

alexandrehtrb opened this issue Sep 23, 2019 · 1 comment


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commented Sep 23, 2019

Tupled returns and outrefs in functions outputs

I propose we allow outrefs in function parameters to be outputted with return statements in tupled form, as it already works with methods.

Example that it works, with methods:

type ClassA() =
    member this.CountAs(s: string, found: outref<bool>): int =
        let num = s.Count(Func<char, bool>((=) 'a'))
        found <- num > 0

let numAs, found = ClassA().CountAs("abcde")

Example that does not work, with functions:

let countAs(s: string, found: outref<bool>): int =
    let num = s.Count(Func<char, bool>((=) 'a'))
    found <- num > 0

let numAs, found = countAs("abcde")

Pros and Cons

The advantage of making this adjustment to F# is more predictability in using tupled outputs with returns and outrefs, because I do not see a reason for this currently only be available for methods, and not functions.

Extra information

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

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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commented Sep 23, 2019

I wouldn't say I'm against this in principle, though the current behavior with methods is rooted in interop with a .NET pattern that isn't very common in purely F# code.

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