[swift-evolution] try?, precedence and double optionals

[Xiaodi Wu]

This question was asked a few months back on this list--I can't recall
exactly when, but there were some useful comments there that would be worth
revisiting.
On Fri, Dec 2, 2016 at 16:16 Tim Vermeulen via swift-evolution <
swift-evolution at swift.org> wrote:

> Given the function
>
> func mightReturnInt() throws -> Any {
>     return 3
> }
>
> combining `try?` and `as?` has a somewhat unexpected result:
>
> if let int = try? mightReturnInt() as? Int {
>     print(int) // => Optional(3)
> }
>
> You’d need to add parentheses to end up with a non-optional:
>
> if let int = (try? mightReturnInt()) as? Int {
>     print(int) // => 3
> }
>
> Apparently, `try?`’s precedence is lower than `as?`’s precedence. Should
> this be changed?
>
> On a similar note:
>
> func mightReturnInt() throws -> Int? {
>     return 3
> }
>
> if let int = try? mightReturnInt() {
>     print(int) // => Optional(3)
> }
>
> Here, `try?` acts as a map, not as a flatMap, resulting in a double
> optional (and in a single optional after unwrapping it). None of the
> possible workarounds are particularly pretty:
>
> if let temp = try? mightReturnInt(), let int = temp {
>     print(int) // => 3
> }
>
> or:
>
> if let int = (try? mightReturnInt()) ?? nil {
>     print(int) // => 3
> }
>
> Once again, is this behaviour expected and desired, or should it be
> changed while it still can?
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> swift-evolution at swift.org
> https://lists.swift.org/mailman/listinfo/swift-evolution
>
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