<html><head><meta http-equiv="Content-Type" content="text/html charset=utf-8"></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><br class=""><div><blockquote type="cite" class=""><div class="">On Jul 29, 2016, at 5:55 PM, Jacob Bandes-Storch <<a href="mailto:jtbandes@gmail.com" class="">jtbandes@gmail.com</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><div dir="ltr" class="">Here are a few thoughts:<div class=""><ul class=""><li class="">-swift=4<br class=""></li><li class="">-swift-version=4<br class=""></li></ul></div></div></div></blockquote><div><br class=""></div><div>-swift-version seems like the best option to me, but Jordan will have a strong opinion. I think he’s crazy busy with Swift 3 work until late next week.</div><div><br class=""></div><div>-Chris</div><div><br class=""></div><br class=""><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><ul class=""><li class="">-language-version=4</li><li class="">a top-of-file "shebang"-style comment indicating the version, something like <font face="monospace, monospace" class="">//#swift(4)</font>, mirroring the "#if swift" syntax</li></ul></div><div class=""><div class="gmail_extra">
<br class=""><div class="gmail_quote">On Fri, Jul 29, 2016 at 5:27 PM, Chris Lattner <span dir="ltr" class=""><<a href="mailto:clattner@apple.com" target="_blank" class="">clattner@apple.com</a>></span> wrote:<br class=""><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex"><div style="word-wrap:break-word" class=""><br class=""><div class=""><span class="gmail-"><blockquote type="cite" class=""><div class="">On Jul 29, 2016, at 5:20 PM, Jacob Bandes-Storch via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank" class="">swift-evolution@swift.org</a>> wrote:</div><br class=""><div class=""><div dir="ltr" class="">Chris writes:<div class=""><blockquote style="margin:0px 0px 0px 0.8ex;border-left:1px solid rgb(204,204,204);padding-left:1ex" class="gmail_quote">- <b class="">Source stability features: </b>These should be relatively small, but important. For example, we need a “-std=swift3” sort of compiler flag. We may also add a way to conditionally enable larger efforts that are under development but not yet stable - in order to make it easier to experiment with them.</blockquote></div><div class=""><br class=""></div><div class=""><br clear="all" class=""><div class=""><div class=""><div dir="ltr" class=""><div class="">I am curious whether the team has thoughts on how to organize the compiler codebase in such a way that new features can be added, and possibly source-breaking changes made, while still keeping the old functionality around.</div><div class=""><br class=""></div><div class="">Are any obvious areas that will need refactoring to make this feasible? (Perhaps they could be turned into StarterBugs.)</div></div></div></div></div></div></div></blockquote><div class=""><br class=""></div></span><div class="">I think this would be a great thing to do. We need a few things:</div><div class=""><br class=""></div><div class="">- The actual compiler flag. It is worth bikeshedding how it is spelled. “-std=“ is good inspiration, but clearly the wrong specific name.</div><div class=""><br class=""></div><div class="">- The implementation should be straight forward: the flag should get plumbed through to a field in swift::LangOptions. Code that diverges can then check it.</div><div class=""><br class=""></div><div class="">- Handling divergence in the standard library is another big issue. We have some ideas here, but it depends on having the compiler work done anyway to hook into.</div><span class="gmail-"><div class=""><br class=""></div><blockquote type="cite" class=""><div class=""><div dir="ltr" class=""><div class=""><div class=""><div class=""><div dir="ltr" class=""><div class="">How many versions back would the compiler be expected to support? Should the Swift 5 compiler still support Swift 3 code?</div></div></div></div></div></div></div></blockquote></span></div><br class=""><div class="">To be determined. Swift 4 should definitely support Swift 3, but Swift 5 perhaps not. We can decide that when Swift 4 is winding down.</div><span class="gmail-HOEnZb"><font color="#888888" class=""><div class=""><br class=""></div><div class="">-Chris</div></font></span></div></blockquote></div><br class=""></div></div></div>
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