<div dir="ltr">Here's real working code you can tinker with in Swift 2.1:<div><br></div><div><p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo;color:rgb(187,44,162)">extension<span style="color:rgb(0,0,0)"> </span><span style="color:rgb(112,61,170)">Indexable</span><span style="color:rgb(0,0,0)"> {</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo"> <span style="color:rgb(187,44,162)">public</span> <span style="color:rgb(187,44,162)">subscript</span>(ifExists index: <span style="color:rgb(112,61,170)">Index</span>) -> <span style="color:rgb(112,61,170)">_Element</span>? {</p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo"> <span style="color:rgb(187,44,162)">get</span> {</p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo"> <span style="color:rgb(187,44,162)">if</span> <span style="color:rgb(112,61,170)">startIndex</span>.<span style="color:rgb(61,29,129)">distanceTo</span>(index) <span style="color:rgb(61,29,129)"><</span> <span style="color:rgb(112,61,170)">startIndex</span>.<span style="color:rgb(61,29,129)">distanceTo</span>(<span style="color:rgb(112,61,170)">endIndex</span>) {</p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo"> <span style="color:rgb(187,44,162)">return</span> <span style="color:rgb(187,44,162)">self</span>[index]</p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo"> }</p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo"> <span style="color:rgb(187,44,162)">return</span> <span style="color:rgb(187,44,162)">nil</span></p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo"> }</p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo"> }</p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo">}</p>
<p style="margin:0px;font-size:11px;line-height:normal;font-family:Menlo"><br></p></div><div>You can make the setter work and factor out some of the ugly if you wanted. I didn't want to. I have no desire to see this in the language. I just wanted to point out that developers who want it can have it today.</div><div><br></div><div>-david <a href="https://github.com/AE9RB/SwiftGL" target="_blank">https://github.com/AE9RB/SwiftGL</a></div></div><div class="gmail_extra"><br><div class="gmail_quote">On Sun, Jan 31, 2016 at 3:21 PM, David Sweeris 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:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div dir="auto"><div>My recollection from the discussion thread is that we didn't really reach a firm consensus on the setter semantics, mostly because Swift doesn't support setter-only subscripts, and we couldn't come up with one argument label that both read well as both a setter & a getter, *and* clearly meant that the assignment itself could fail.</div><div><br></div><div>Don't misunderstand me... I'm definitely +1 on this, I'm just not a fan of "ifExists" (no, I don't have any better ideas)</div><div><br>- Dave Sweeris</div><div><div class="h5"><div><br>On Jan 31, 2016, at 15:07, Maximilian Hünenberger via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>> wrote:<br><br></div><blockquote type="cite"><div><div></div><div>The setter of the subscript should be:</div><div><div><div dir="auto"><div><div><div><div style="word-wrap:break-word"><div><div><blockquote style="margin:0px 0px 0px 40px;border:none;padding:0px"><div><div style="margin:0px;line-height:normal"><div style="margin:0px;line-height:normal"><font color="#000000"><span style="background-color:rgba(255,255,255,0)"><span><br></span></span></font></div><div style="margin:0px;line-height:normal"><font color="#000000"><span style="background-color:rgba(255,255,255,0)"><span>set</span> {</span></font></div><div style="margin:0px;line-height:normal"><font color="#000000"><span style="background-color:rgba(255,255,255,0)"> <span>if</span> <span>self</span>.indices ~= index && newValue != <span>nil</span> {</span></font></div><div style="margin:0px;line-height:normal"><font color="#000000"><span style="background-color:rgba(255,255,255,0)"> <span>self</span>[index] = newValue!</span></font></div><div style="margin:0px;line-height:normal"><font color="#000000"><span style="background-color:rgba(255,255,255,0)"> }</span></font></div><div style="margin:0px;line-height:normal"><font color="#000000"><span style="background-color:rgba(255,255,255,0)">}</span></font></div><div style="margin:0px;line-height:normal"><font color="#000000"><span style="background-color:rgba(255,255,255,0)"><br></span></font></div><div style="margin:0px;line-height:normal"><font color="#000000"><span style="background-color:rgba(255,255,255,0)">Since "newValue" is of type "Element?".</span></font></div><div style="margin:0px;line-height:normal"><br></div><div style="margin:0px;line-height:normal">It seems that this subscript could also be added to "CollectionType" and "MutableCollectionType".</div><div style="margin:0px;line-height:normal"><br></div><div style="margin:0px;line-height:normal">The setter is weird because you can use an optional element:</div><div style="margin:0px;line-height:normal"><br></div><div style="margin:0px;line-height:normal">var arr = [1]</div><div style="margin:0px;line-height:normal">// is valid but doesn't set the first element</div><div style="margin:0px;line-height:normal">arr[ifExists: 0] = nil</div><div style="margin:0px;line-height:normal"><br></div><div style="margin:0px;line-height:normal">var arr2: [Int?] = [1]</div><div style="margin:0px;line-height:normal">arr2[ifExists: 0] = nil // changes nothing</div><div style="margin:0px;line-height:normal">arr2[ifExists: 0] = .Some(nil) // sets first element to nil : arr2 == [nil]</div><div style="margin:0px;line-height:normal"><br></div><div style="margin:0px;line-height:normal">I don't know whether a setter should be added at all.</div><div style="margin:0px;line-height:normal"><br></div><div style="margin:0px;line-height:normal">- Maximilian</div></div></div></blockquote></div></div></div></div></div></div></div></div></div><div><br>Am 31.01.2016 um 23:38 schrieb Rudolf Adamkovič via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>>:<br><br></div><blockquote type="cite"><div><div>All right, I put together a proposal:</div><div><br></div><div><a href="https://github.com/salutis/swift-evolution/blob/master/proposals/XXXX-runtime-safe-array-subscripting.md" target="_blank">https://github.com/salutis/swift-evolution/blob/master/proposals/XXXX-runtime-safe-array-subscripting.md</a></div><div><br></div><div>… and opened a PR:</div><div><br></div><div><a href="https://github.com/apple/swift-evolution/pull/133" target="_blank">https://github.com/apple/swift-evolution/pull/133</a></div><div><br></div><div>Let’s see how this goes.</div><div><br></div><div>R+</div></div></blockquote></div></blockquote></div></div><blockquote type="cite"><div><span>_______________________________________________</span><span class=""><br><span>swift-evolution mailing list</span><br><span><a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a></span><br><span><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br></span></div></blockquote></div><br>_______________________________________________<br>
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