> On 29 Jun 2017, at 09:19, Elviro Rocca via swift-evolution > <[email protected]> wrote: > > >> Il giorno 29 giu 2017, alle ore 03:18, Ben Cohen via swift-evolution >> <[email protected]> ha scritto: >> >> Finally, there’s a woolier justification: there’s an often-touted >> misconception out there that force unwraps are bad, that they were only >> created to accommodate legacy apps, and that force-unwrapping is always bad >> and you should never do it. This isn’t true – there are many good reasons to >> use force unwrap (though if you reaching for it constantly it’s a bad sign). >> Force-unwrapping is often better than just whacking in a default value or >> optional chaining when the presence of nil would indicate a serious failure. >> Introduction of the `!!` operator could help endorse/encourage the use of >> “thoughtful” force-unwrapping, which often comes with a comment of the >> reasoning why it’s safe (of why the array can’t be empty at this point, not >> just that it is empty). And if you’re going to write a comment, why not make >> that comment useful for debugging at the same time. >> > > If one could still just "!" I'm not sure that the "!!" would really encourage > a more thoughtful force unwrapping. Almost every crash related to a force > unwrap that I see from Swift beginners is 100% due to the fact that adding > and exclamation point makes the code compile, so they add it. > > Also, I strongly disagree with your statement that the idea that > force-unwraps are bad is a misconception: if something is Optional, there's a > reason why it is, otherwise it would not be Optional at all, and that's the > reason why Optional exists in Swift and represents a substantial > technological advancement over Objective-C. Using an Optional means that we > are actually adding a thoughtful information to an instance: it could be > there, or it could not, and that's perfectly fine. Crashing an app in > production for a force-unwrap results in the poorest user experience ever, > and it should never happen.
If forced unwraps are only used in instances where you specifically expect the optional to not be nil, it is essentially sugar for a guard with preconditionFailure: it is used to enforce invariants the app should never break. It is very similar to a trap when accessing an out of bounds index in an array. In those cases, I actually prefer it crashing than having the app silently fail for the user, and you never finding out. I try to limit my use of optional unwrapping but there are sometimes quite useful. IMHO, they are not inherently bad, but can be badly used. > I feel compelled to link another article, where Soroush Khanlou shows that > sometimes the bare semantics of an Optional (that is, something is there or > not) is not enough: http://khanlou.com/2017/03/that-one-optional-property/ > > I also disagree with the idea that the "?? fatalError()" alternative suffers > from cognitive dissonance, for the following reasons: > > - on the right of the "??" operator there could be both an Optional or a > non-Optional, which would result in a different type for the resulting > instance; > - fatalError() by itself is an operation that changes the meaning of a > function, making it non-total, and its very name conveys a clear meaning to a > person that reads the code, thus it really doesn't seem to me that "?? > fatalError()" could be misinterpreted; > > Anyway, it would be interesting to consider "!! message" as an alternative to > "!", thus forcing the user to at least do extra effort: that could discourage > a light use of !. > > > Elviro > _______________________________________________ > swift-evolution mailing list > [email protected] > https://lists.swift.org/mailman/listinfo/swift-evolution
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