[swift-evolution] [Pitch] Make try? + optional chain flattening work together

[Nevin Brackett-Rozinsky]

This is not an optional-chaining issue *per se*. If you simply write,

let a = try? SomeType().doThrow()

// a has type SomeType??

you get a double-optional as well. Are you proposing to change that?

Nevin


On Fri, Jan 12, 2018 at 12:25 PM, Russ Bishop via swift-evolution <
swift-evolution at swift.org> wrote:

> Greetings swift-evolution!
>
> There is currently a disconnect between optional chaining and try? when it
> comes to optional flattening:
>
>
> struct SomeType {
>     func nonThrow() -> SomeType? { return self }
>     func doThrow() throws -> SomeType? { return self }
>     func nonOptional() throws -> SomeType { return self }
> }
>
> let w = SomeType().nonThrow()?.nonThrow()?.nonThrow()?.nonThrow()
> // w has type SomeType?
>
> let x = try? SomeType().nonOptional().nonOptional().nonOptional().nonOpti
> onal()
> // x has type SomeType?
>
> let y = try! SomeType().doThrow()?.doThrow()?.doThrow()?.doThrow()
> // y has type SomeType?
>
> let z = try? SomeType().doThrow()?.doThrow()?.doThrow()?.doThrow()
> // z has type SomeType??
>
>
> We get a double-optional only when combining try? and optional-chaining.
> That is inconvenient and it would be natural to have the compiler do the
> flattening here.
>
>
> If anyone is interested in working on the proposal or implementation
> please let me know. It would make a nice self-contained task if you're
> looking to start contributing.
>
>
> Russ Bishop
>  Simulator
>
>
>
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> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
>
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