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<body><div>Understood. Luckily we had a pretty decent test suite that caught this. Thanks for working through that with me Philippe.</div>
<div><br></div>
<div>On Thu, Aug 24, 2017, at 03:35 PM, Philippe Hausler wrote:<br></div>
<blockquote type="cite"><div>This is expected behaviors of collections and their slices. The previous result was a bug.<br></div>
<div><br></div>
<div><div>I agree that collections in general and their slices need more documentation.<br></div>
<div><br></div>
<div>Sent from my iPhone<br></div>
</div>
<div><div><br></div>
<div>On Aug 24, 2017, at 11:28 AM, Ryan Lovelett <<a href="mailto:swift-dev@ryan.lovelett.me">swift-dev@ryan.lovelett.me</a>> wrote:<br></div>
</div>
<blockquote type="cite"><div><div>I think your onto it Philippe but then why is it behaving that way?<br></div>
<div><br></div>
<div>I updated my earlier script (attached) and added 2 things.<br></div>
<div><br></div>
<div> 1. print("Start: \(data.startIndex), End: \(data.endIndex), Count: \(data.count)") after the data.removeFirst(4).<br></div>
<div> 2. The startIndex offset you suggested.<br></div>
<div><br></div>
<div>It no longer crashes. Hooray!<br></div>
<div><br></div>
<div>Swift 3.1:<br></div>
<div><br></div>
<div>Start: 0, End: 2, Count: 2<br></div>
<div>Base64: QWE=, String: Aa<br></div>
<div><br></div>
<div>Swift 3.2:<br></div>
<div><br></div>
<div>Start: 4, End: 6, Count: 2<br></div>
<div>Base64: QWE=, String: Aa<br></div>
<div><br></div>
<div>Oh wait. Woah. That's a really subtle change that has some very real consequences.<br></div>
<div><br></div>
<div>Is this expected and/or documented? Because I certainly would not have expected that drastic of a change. I'll obviously need to go read a lot more of the changes between Swift 3.1 and Swift 3.2 if these sorts of changes are in scope.<br></div>
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<div><br></div>
<div>On Thu, Aug 24, 2017, at 02:10 PM, Philippe Hausler wrote:<br></div>
<blockquote type="cite"><div>I see the issue.. the latest version traps (appropriately so).<br></div>
<div><div><br></div>
<div><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px;font-stretch:normal;font-size:14px;line-height:normal;font-family:Menlo;color:rgb(237, 232, 229);background-color:rgb(43, 43, 43);"><span class="colour" style="color:rgb(253, 67, 132)">let</span> str = <span class="colour" style="color:rgb(238, 219, 4)">String</span>(bytes: <span class="colour" style="color:rgb(118, 224, 242)">data</span>[<span class="colour" style="color:rgb(245, 127, 255)">0</span>..<<span class="colour" style="color:rgb(245, 127, 255)">2</span>], encoding: .<span class="colour" style="color:rgb(118, 224, 242)">utf8</span>)!<br></div>
<div><div><br></div>
<div>The sub-range of the slice you have is incorrectly indexed. Try this out (I am presuming this is what you mean):<br></div>
<div><br></div>
<div><div style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0px;font-stretch:normal;font-size:14px;line-height:normal;font-family:Menlo;color:rgb(237, 232, 229);background-color:rgb(43, 43, 43);"><span class="colour" style="color:rgb(253, 67, 132)">let</span> str = <span class="colour" style="color:rgb(238, 219, 4)">String</span>(bytes: <span class="colour" style="color:rgb(118, 224, 242)">data</span>[<span class="colour" style="color:rgb(118, 224, 242)">data</span>.<span class="colour" style="color:rgb(118, 224, 242)">startIndex</span>..<(<span class="colour" style="color:rgb(118, 224, 242)">data</span>.<span class="colour" style="color:rgb(118, 224, 242)">startIndex</span> + <span class="colour" style="color:rgb(245, 127, 255)">2</span>)], encoding: .<span class="colour" style="color:rgb(118, 224, 242)">utf8</span>)!<br></div>
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<div><div><br></div>
<blockquote type="cite"><div>On Aug 24, 2017, at 11:07 AM, Philippe Hausler <<a href="mailto:phausler@apple.com">phausler@apple.com</a>> wrote:<br></div>
<div><br></div>
<div><div><div>Is there a radar or <a href="http://bugs.swift.org">bugs.swift.org</a> ticket filed on this?<br></div>
<div><br></div>
<div>I presume because of the import this is a Darwin thing and not a linux thing.<br></div>
<div><br></div>
<blockquote type="cite"><div>On Aug 24, 2017, at 11:05 AM, Michael Gottesman via swift-dev <<a href="mailto:swift-dev@swift.org">swift-dev@swift.org</a>> wrote:<br></div>
<div><br></div>
<div><br></div>
<blockquote type="cite"><div>On Aug 24, 2017, at 10:47 AM, Ryan Lovelett via swift-dev <<a href="mailto:swift-dev@swift.org">swift-dev@swift.org</a>> wrote:<br></div>
<div><br></div>
<div>I've found what I believe is a bug. Though I'm unclear if the bug is in<br></div>
<div>Swift 3.1 or Swift 3.2/4.0. All I can say for sure is the behavior is<br></div>
<div>quite drastically different between the two.<br></div>
<div><br></div>
<div>For the code below (and attached):<br></div>
<div><br></div>
<div> import Cocoa<br></div>
<div><br></div>
<div> var data = Data(bytes: [0x50, 0x4B, 0x01, 0x02, 0x41, 0x61])<br></div>
<div> data.removeFirst(4)<br></div>
<div> let base64 = data.base64EncodedString()<br></div>
<div> let str = String(bytes: data[0..<2], encoding: .utf8)!<br></div>
<div> print("Base64: \(base64), String: \(str)")<br></div>
<div><br></div>
<div>If I compile and run that with the Swift included in Xcode 8.3.3 (e.g.,<br></div>
<div>swift ./data-bug.swift) it outputs: Base64: QWE=, String: Aa. Which is<br></div>
<div>what I expect.<br></div>
<div><br></div>
<div>With the Swift that is included with Xcode 9.0 beta 6 (9M214v) (e.g.,<br></div>
<div>swift -swift-version 3 ./data-bug.swift). It performs an illegal<br></div>
<div>hardware instruction and crashes. It also does this if I use use the<br></div>
<div>version 4 of the compiler.<br></div>
<div><br></div>
<div>Is this a bug? If so where is the bug? Was this always meant to not work<br></div>
<div>and Swift 3.1 just happened to work or is there now an issue in the<br></div>
<div>Swift 3.2 implementation?<br></div>
</blockquote><div><br></div>
<div>I have not engaged my brain with the particulars of the rest of the email, but high level question: does this happen without optimization? Or does it happen only with optimization?<br></div>
<div><br></div>
<div>Michael<br></div>
<div><br></div>
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</blockquote><blockquote type="cite"><div><data-bug.swift><br></div>
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