On Fri, Jun 30, 2017 at 7:24 AM, Brent Royal-Gordon via swift-evolution < swift-evolution@swift.org> wrote:
> 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. > +1 to everything. If terseness is the only clear advantage of a new operator that is meant to be used sparsely, it's clear to me that the ?? Never form is better for the Swift community as a whole. -- Víctor Pimentel
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