Just spit-balling here, but couldn’t you do this with a generic extension on
Optional?
> extension Optional {
> func returnsNil(errorCode: Int) -> Wrapped? {
> logError(errorCode)
> return nil
> }
> }
Jeff Kelley
[email protected] | @SlaunchaMan <https://twitter.com/SlaunchaMan> |
jeffkelley.org <http://jeffkelley.org/>
> On Jan 3, 2016, at 10:43 PM, Andrew Duncan via swift-evolution
> <[email protected]> wrote:
>
> It should be possible to declare a function that returns only nil, and have
> its return type be substitutable for any function that returns and Optional.
> This is something like having a bottom type but not really. What I mean is:
>
> func returnsNil(errCode:Int) -> nil {
> logError(errCode) // A side-effect. Not FP, sosumi.
> return nil
> }
>
> func returnAOptional() -> A? {
> // Bla bla. We discover an error so we decide to bail and return nil.
> return returnsNil(errCode) // Would be legal.
> }
> func returnsBOptional() -> B? {
> // Bla bla. We discover an error so we decide to bail and return nil.
> return returnsNil(errCode) // Would also be legal.
> }
>
> I seek a return type that conforms to any Optional -- I think that implies it
> *must* (or correct me here) be nil.
>
> Now perhaps this is already possible with wizardry from the Next Level.
> (There always is one.)
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