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<body><div>On Tue, Oct 4, 2016, at 10:28 AM, Nate Cook wrote:<br></div>
<blockquote type="cite"><div><blockquote type="cite"><div>On Oct 3, 2016, at 5:49 PM, Kevin Ballard via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br></div>
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<div><div><div>On Mon, Oct 3, 2016, at 03:18 PM, Jordan Rose wrote:<br></div>
<blockquote type="cite"><div><blockquote type="cite"><div><br></div>
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</blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite">...<br></blockquote></blockquote></blockquote><blockquote type="cite"><blockquote type="cite"><blockquote type="cite"><br></blockquote></blockquote></blockquote><blockquote type="cite"><div><div><blockquote type="cite"><div>We had this at one point, but we took it out because people would forget to test the nil case. I think `?? ""` or `?? nil` really is the best answer here.<br></div>
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<div>But you can't write that, unless you're dealing specifically with an Optional<String>. If you try you'll get an error:<br></div>
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<div><span class="font" style="font-family:menlo, consolas, monospace, sans-serif">unnamed.swift:2:19: error: binary operator '??' cannot be applied to operands of type 'Int?' and 'String'</span><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"> print("x: \(x ?? "nil")")</span><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"> ~ ^ ~~~~~</span><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, monospace, sans-serif">unnamed.swift:2:19: note: overloads for '??' exist with these partially matching parameter lists: (T?, @autoclosure () throws -> T), (T?, @autoclosure () thro</span><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, monospace, sans-serif">ws -> T?)</span><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"> print("x: \(x ?? "nil")")</span><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"> ^</span><span class="font" style="font-family:menlo, consolas, monospace, sans-serif"></span><br></div>
<div>This leads to writing code like "… \(x.map(String.init(describing:)) ?? "nil")" which is pretty gross.<br></div>
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<div>I think that if we're going to add this warning we should make it possible to provide a string as an alternative. It seems like it should be possible to build a <span class="font" style="font-family:Menlo">??</span> operator with a <span class="font" style="font-family:Menlo">(T?, String) -> _StringInterpolationSomething</span> signature that works only in a string interpolation context.<br></div>
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<div>There are some types that aren't trivially constructible, or don't have clear alternatives for the nil case. Other times it might just not make sense to build a new instance simply to turn it into a string. If we're going to make people provide an alternative for optionals in this otherwise simple-to-use construct, let's make it simple to do so.<br></div>
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<div>This is undoubtedly a more complex approach that could be considered separately, but I think it would be a valuable part of how developers could transition their code.<br></div>
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<div>I like this idea. This combined with the warning for naively interpolating an Optional would be a good solution, because now when I see the warning I can trivially solve it with `?? "nil"`.<br></div>
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<div>-Kevin Ballard</div>
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