<div dir="ltr">Or perhaps some subscripts with parameter labels, like<div><br></div><div>extension Array {</div><div> subscript(fromEnd distance: Int) -> Element {</div><div> return self[endIndex - distance]</div><div> }</div><div>}</div><div><br></div><div>[0, 1, 2][fromEnd: 1] // returns 2</div><div class="gmail_extra"><br clear="all"><div><div><div dir="ltr"><div>Jacob Bandes-Storch<br></div></div></div></div>
<br><div class="gmail_quote">On Fri, Dec 18, 2015 at 1:46 PM, Joe Groff via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0px 0px 0px 0.8ex;border-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:solid;padding-left:1ex"><div style="word-wrap:break-word"><span><br><div><blockquote type="cite"><div>On Dec 18, 2015, at 4:42 AM, Amir Michail via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>> wrote:</div><br><div><div style="word-wrap:break-word">Examples:<div><br></div><div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">>>> l=[1,2,3,4,5]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">>>> l[-1]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">5</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">>>> l[-2]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">4</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">>>> l[2:4]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">[3, 4]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">>>> l[2:]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">[3, 4, 5]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">>>> l[-2:]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">[4, 5]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">>>> l[:3]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">[1, 2, 3]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">>>> l[::2]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">[1, 3, 5]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">>>> l[::]</div><div style="margin:0px;font-size:16px;line-height:normal;font-family:Menlo">[1, 2, 3, 4, 5]</div></div>
</div></div></blockquote><br></div></span><div>Accepting negative indices is problematic for two reasons: it imposes runtime overhead in the index operation to check the sign of the index; also, it masks fencepost errors, since if you do foo[m-n] and n is accidentally greater than m, you'll quietly load the wrong element instead of trapping. I'd prefer something like D's `$-n` syntax for explicitly annotating end-relative indexes.</div><div><br></div><div>-Joe</div><br>
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