+1 Well summarized.
The !! operator feels more like:
func !! <T>(optional: T?, errorMessage: String) -> T {
return optional ?? fatalError(errorMessage)
}
Which is totally unnecessary.
--
Adrian Zubarev
Sent with Airmail
Am 30. Juni 2017 um 07:24:04, Brent Royal-Gordon via swift-evolution
(swift-evolution@swift.org) schrieb:
On Jun 27, 2017, at 10:16 AM, Erica Sadun via swift-evolution
<swift-evolution@swift.org> wrote:
Using an operator to provide feedback on the context of a failed unwrap has
become a commonly implemented approach in the Swift developer Community. What
are your thoughts about adopting this widely-used operator into the standard
library?
guard !lastItem.isEmpty else { return }
let lastItem = array.last !! "Array must be non-empty"
Details here: https://gist.github.com/erica/423e4b1c63b95c4c90338cdff4939a9b
Thank you for your thoughtful feedback, -- E
Finally found a few minutes to read this thread.
I'm a big fan of the `Never`-based approach. (I was before, but I am more so
now.) Here are the points I can see in its favor:
1. It is extremely clear about what's happening—`!!` is another random operator
to learn, but `fatalError(_:)` or `preconditionFailure(_:)` are fairly
self-explanatory, and `??` is something you might already be using.
2. It allows you to control the optimization behavior by using `fatalError`,
`preconditionFailure`, or `assertionFailure` as desired.
3. If we later change `throw` from being a statement to being a
`Never`-returning expression, you could use `throw` on the right-hand side of
`??`.
4. It supports other `Never`-returning operations, like `abort()` or `exit(_:)`
or your custom `usage()` function, on the right side of `??`.
5. It supports file-and-line error reporting without having to add any new
features; `!!` could not do this because an operator can't have extra,
defaulted parameters to carry the file and line.
6. It harmonizes with the eventual idea of making `Never` a universal bottom
type, but we don't actually have to implement that today, because we can just
overload `??` for now.
Against these advantages, the only one I can see for `!!` is that it is terse.
Terseness is good, especially for a feature which is competing with the
single-character postfix `!` operator, but I can't help but be drawn to the
flexibility and power of `??` with a `Never` expression on the right-hand side.
--
Brent Royal-Gordon
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