How about this?
func withPredicateErrors<Element, Return>(
_ predicate: @escaping (Element) throws -> Bool,
do body: ((Element) -> Bool) -> Return
) rethrows
-> Return
{
var caught: Error?
var element: Element?
let value = body { elem in
element = elem
do {
return try predicate(elem)
}
catch {
caught = error
return true // Terminate search
}
}
if let _ = caught,
let element = element {
try _ = predicate(element)
}
return value
}
-Kenny
> On Dec 30, 2017, at 8:15 PM, Brent Royal-Gordon via swift-users
> <[email protected]> wrote:
>
> I need to do something like this:
>
> func withPredicateErrors<Element, Return>(_ predicate: (Element) throws
> -> Bool, do body: ((Element) -> Bool) -> Return) rethrows -> Return {
> var caught: Error?
> let value = body { elem in
> do {
> return try predicate(elem)
> }
> catch {
> caught = error
> return true // Terminate search
> }
> }
>
> if let caught = caught {
> throw caught
> }
> else {
> return value
> }
> }
>
> The problem is, the Swift compiler doesn't allow the explicit `throw`
> statement; even though it can only throw errors originally thrown by
> `predicate`, the compiler is not smart enough to prove that to itself. I
> cannot make `body` a `throws` function.
>
> Is there any way to do this? Either to override the compiler's safety check,
> or to rewrite this function to avoid it?
>
> --
> Brent Royal-Gordon
> Architechies
>
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