<div dir="ltr"><br><div class="gmail_quote"><div dir="ltr"><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">I've occasionally hit this problem too, but I don’t think it warrants a language addition, as it can be overcome in other ways. I would move the expensive calculation into its own private method and rewrite your example like this:</div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><br></div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="white-space:pre-wrap"> </span>return cachedValue ?? calculatedValue()</div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><br></div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">In my opinion that would fit better with the single responsibility principle and make unit testing easier.</div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><br></div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">John</div><div style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><br></div><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> -1 as there IMO some confusion between all these `not` and `else` and the</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> meaning of the expression at all is not obvious for me: "check that not</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> allowed to assign _someExpensiveResult to some instance cachedValue,</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> otherwise return something"</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> This really looks nice, clean and obvious :</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> guard cachedValue == nil else {</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> // here you need just to fast return unwrapped value of cachedValue</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> // so, IMO unwrapping it in this block is OK</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> return cachedValue!</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> }</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> // here you want to have cachedValue == nil, so you'll need to unwrap</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> it(after assignment) in any case.</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> What I can see as improvement in this direction, something like this:</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> guard cachedValue == nil else let cachedValue! {</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> // here you can use unwrapped cachedValue</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> return cachedValue</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> }</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> Hmm... Btw, what about improving in optional binding: It is common to</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> shadow optional value name with unwrapped value with same name:</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> if let value = value {...} // too much noise</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> What about introduce such syntax:</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> if let value! {</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> // unwrapped value here</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> }</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> Seems like clear and obvious about what does this mean. Opinions? (before I</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> drop this to separate thread)</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> On 14.05.2016 8:52, Karl via swift-evolution wrote:</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > If we want to check that an optional has a value and bail if it doesn't, we have the helpful pattern:</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > guard let x = x else { throw SomeError }</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > However, it is also fairly common that you want to check that an optional *is* nil, and still bail if it isn’t (maybe using the value that you now know exists), e.g:</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > guard cachedValue == nil else { return cachedValue! }</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > cachedValue = //… expensive calculation</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > It seems a little bit “unfair” that we have this lovely clean `let` syntax when checking for Optional.Some, but we to have to do this ugly manual check against nil and explicit unwrap when checking for Optional.None. There is literally no other way to satisfy the guard statement; our optional bindings only go one-way can’t be evaluated.</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > What about if we introduced a “not” modifier to optional bindings?</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > guard not let cachedValue = _someExpensiveResult else { return cachedValue }</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > This obviously wouldn’t make sense for “if let…” switching, as the variables get bound in the ‘else’ block and the code wouldn’t be very readable. For the special case of a guard statement, though, which only has an ‘else’ block, it does make some sense.</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > If we had something like this, certainly in my code, I’d be able to eliminate almost all (maybe even all) remaining force-unwraps of optionals; that’s great! It’d be amazing if the language was expressive enough that you could go without ever having to force-unwrap an optional. And it just makes sense.</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > Thoughts?</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > Karl</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > _______________________________________________</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > swift-evolution mailing list</span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > swift-evolution at <a href="http://swift.org" target="_blank">swift.org</a></span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> > <a href="https://lists.swift.org/mailman/listinfo/swift-evolution" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">> </span><br style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px"><span style="color:rgb(0,0,0);font-family:Helvetica;font-size:12px">></span> <br></div>
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