I actually half agree with you that this behaviour would be conceptually
related to the do-catch block (although not a specific catch statement). So
maybe alternatively the shorthand for this-
do {
try throwingFunction()
} catch MyError.TheError {
// do something
} catch {
fatalError("Expected error?")
}
could be instead-
do! {
try throwingFunction()
} catch MyError.TheError {
// do something
}
This would also avoid any conflict with existing behaviour.
Cheers,
Simon
> On 6 May 2017, at 1:26 pm, Xiaodi Wu <xiaodi...@gmail.com> wrote:
>
> _If_ this is something that's important, then the ! should follow 'catch' and
> not 'try'.
>
> The keyword 'try!' already means something, and it's not that. People may
> already mix try! and try in a do block and the behavior cannot be changed for
> source compatibility.
> On Sat, May 6, 2017 at 15:16 Simon Pilkington via swift-evolution
> <swift-evolution@swift.org <mailto:swift-evolution@swift.org>> wrote:
> As a number of recent threads have shown, typed throws and error handling is
> a complicated topic with a lot of implications.
>
> However in the mean time we could potentially address one of the pain points
> people give for wanting typed throws - exhaustive catch statements.
>
> For functions that you completely control, it is possible to be completely
> certain of the errors the function will throw and it is an unrecoverable
> logical error for any other error to be thrown. Currently this situation
> would have to be handled like so-
>
> do {
> try throwingFunction()
> } catch MyError.TheError(let theContext) {
> // do something
> } catch {
> fatalError(“Impossible error?")
> }
>
> Here, the catch-all is just boilerplate to make the catch statement
> exhaustive but doesn’t provide any value to the programmer. Would it make
> sense to provide a shorthand for this case like this-
>
> do {
> try! throwingFunction()
> } catch MyError.TheError(let theContext) {
> // do something
> }
>
> Where the try! still indicates the call could fatalError if the function
> throws an unmatched error but allows the programmer to specify the errors
> that they specifically want to handle. I don’t think this moves the language
> away from the possibility of typed throws; adding typed throws would likely
> cause a warning in both cases - either to remove the catch-all or all the ! -
> if the compiler could determine the catch was now exhaustive without them.
>
> If this has been proposed elsewhere I apologise.
>
> Cheers,
> Simon
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