> Le 4 mai 2016 à 08:28, Pyry Jahkola via swift-evolution
> <[email protected]> a écrit :
>
> Here's my review of "SE-0073: Marking closures as executing exactly once".
>
>> What is your evaluation of the proposal?
>
> +1. I think this is a good idea and should be accepted (without extending the
> proposed scope).
>
> However, I think the proposal should be more explicit about the case when
> (and whether) the block itself throws. Specifically, I think we should
> highlight that the criterion that
>
>> it must not be executed on any path that throws
>
> implies that a @noescape(once) parameter itself cannot throw (until another
> language change allows otherwise).
>
> […]
>
> Being able to throw out of a @noescape(once) block […] would complicate the
> language by requiring that no one catches the error in the scope where
> uninitialised variables are defined. I suggest adding this remark to the
> Future directions.
Hello Pyry,
I quite expect being able to throw out of a @noescape(once) block. Maybe the
sentence "it must not be executed on any path that throws" should be removed
from the proposal, should it have the implications you describe.
Here is below what I expect this proposal to allow. So you see one problematic
case?
// Function which rethrows closure errors:
func f1(closure: @noescape(once) () throws -> ()) rethrows {
try closure()
}
// Function which may throw before, inside, or after the closure:
func f2(closure: @noescape(once) () throws -> ()) throws {
try mayFailBefore()
try closure()
try mayFailAfter()
}
// Support function
func getX() throws -> Int { return 1 }
Case 1:
let x: Int
f1 {
x = 1
// use x
}
// use x
Case 2:
let x: Int
do {
try f1 {
x = try getX()
// use x
}
// use x
} catch {
// can't use x
}
// can't use x
Case 3:
let x: Int
do {
try f1 {
x = try getX()
// use x
}
// use x
} catch {
x = 1
}
// use x
Case 4:
let x: Int
do {
try f2 {
x = try getX()
// use x
}
// use x
} catch {
// can't use x
}
// can't use x
Case 5:
let x: Int
do {
try f2 {
x = try getX()
// use x
}
// use x
} catch {
x = 1
}
// use x
Gwendal Roué
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