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.send { color:#77bb77; }
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.error { color:#AA0000; }</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div class="bloop_markdown"><p>Okay this is a view, but this design also implies multiple copies of the array, for the getter and even more for the setter, which could be expensive in some cases.</p>
<p>However the named subscript would allow me to mutate in-place. </p>
<p>Plus another side-effect of such a view design is the ability of replacing the whole storage by swapping out two similar typed views.</p>
<pre><code class="swift">var string1 = "hello"
var string2 = "goodbye"
let chars1 = string1.characters
let chars2 = string2.characters
string1.characters = chars2
string2.characters = chars1
// string1 == "goodbye"
// string2 == "hello"
</code></pre>
<p></p></div><div class="bloop_original_html"><style>body{font-family:Helvetica,Arial;font-size:13px}</style><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div> <br> <div id="bloop_sign_1479457293736585984" class="bloop_sign"><div style="font-family:helvetica,arial;font-size:13px">-- <br>Adrian Zubarev<br>Sent with Airmail</div></div> <br><p class="airmail_on">Am 18. November 2016 um 09:19:20, Xiaodi Wu (<a href="mailto:xiaodi.wu@gmail.com">xiaodi.wu@gmail.com</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>
<title></title>
<div dir="ltr">I believe Dave had a design more like this in mind:
<div><br></div>
<div>```<br>
<div>
<div>struct _View<T> {</div>
<div> let array: Array<Any></div>
<div> subscript(index: Int) -> T? {</div>
<div> guard index >= 0 &&
index < array.count else { return nil }</div>
<div> return array[index] as? T</div>
<div> }</div>
<div>}</div>
<div><br></div>
<div>extension Array {</div>
<div> var double: _View<Double> {</div>
<div> return _View(array: self)</div>
<div> }</div>
<div>}</div>
</div>
<div>```</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Fri, Nov 18, 2016 at 2:00 AM, Adrian
Zubarev 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:1px solid rgb(204,204,204);padding-left:1ex">
<div style="word-wrap:break-word">
<div class="gmail-m_-4091591652219577513m_-7333948024739528437bloop_markdown">
<p>Hi Dave,</p>
<p>Thank you for your answer. I have to admit this is a
‘workaround’ but it will make everything even worse.</p>
<p>From:</p>
<pre><code class="gmail-m_-4091591652219577513m_-7333948024739528437swift">public func scopedJavaScript(at index: Int) -> (javaScript: String, scope: Document)?
</code></pre>
<p>To:</p>
<pre><code class="gmail-m_-4091591652219577513m_-7333948024739528437swift">public subscript(at index: Int) -> (javaScript: String, scope: Document)?
public var scopedJavaScript: Array {
get { return self }
set { /* implementation artifact */ }
}
</code></pre>
<p>Now I could write code like
<code>array.scopedJavaScript.scopedJ<wbr>avaScript.scopedJavaScript</code>
and so one, which makes no sense any more.</p>
<p>Where we could simply allow:</p>
<pre><code class="gmail-m_-4091591652219577513m_-7333948024739528437swift">public subscript scopedJavaScript(at index: Int) -> (javaScript: String, scope: Document)?
</code></pre>
<p>This would ensure that the user can only write something
like:</p>
<pre><code class="gmail-m_-4091591652219577513m_-7333948024739528437swift">array.scopedJavaScript[at: 42] // get the value
array.scopedJavaScript[at: 42] = (…, …) // set the value
</code></pre>
<ul>
<li>Is there anything that speaks against optionally named
subscripts?</li>
<li>Technical reasons?</li>
<li>Swiftiness?</li>
</ul>
</div>
<div class="gmail-m_-4091591652219577513m_-7333948024739528437bloop_original_html">
<div id="gmail-m_-4091591652219577513m_-7333948024739528437bloop_customfont" style="font-family:helvetica,arial;font-size:13px;color:rgb(0,0,0);margin:0px">
<span><br></span></div>
<span><br></span>
<div id="gmail-m_-4091591652219577513m_-7333948024739528437bloop_sign_1479455258346931968" class="gmail-m_-4091591652219577513m_-7333948024739528437bloop_sign">
<div style="font-family:helvetica,arial;font-size:13px">
<span>-- <br>
Adrian Zubarev<br>
Sent with Airmail</span></div>
</div>
<span><br></span>
<div>
<div class="gmail-m_-4091591652219577513h5">
<p class="gmail-m_-4091591652219577513m_-7333948024739528437airmail_on">Am
17. November 2016 um 23:33:44, Dave Abrahams via swift-evolution
(<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>) schrieb:</p>
<blockquote type="cite" class="gmail-m_-4091591652219577513m_-7333948024739528437clean_bq">
<div>
<div><span><br>
on Thu Nov 17 2016, Adrian Zubarev <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>> wrote:<br>
<br>
> Dear Swift community,<br>
><br>
> while building a framework for BSON I had the following
idea.<br>
><br>
> Here is a snippet of some code I do have in my module:<br>
><br>
> extension Array where Element == Document.Value {<br>
><br>
> public func double(at index: Int) -> Double? {<br>
><br>
> guard self.startIndex <= index && index <
self.endIndex else { return nil }<br>
><br>
> if case .double(let double) = self[index] {<br>
><br>
> return double<br>
> }<br>
> return nil<br>
> }<br>
><br>
> …<br>
> }<br>
> This function is used to query the array and check if the
element at the given index is of a<br>
> specific type. Now I would like also to implement a
semi-schema setter.<br>
><br>
> The problem that I see, is the ugliness of the subscript I’d
create.<br>
><br>
> Currently the code would read nicely let d = array.double(at:
42), but after change to a subscript<br>
> the API would look odd array[doubleAt: 42] = 5.0.<br>
><br>
> Don’t get me wrong here, I also have methods with larger names
like public func scopedJavaScript(at<br>
> index: Int) -> …. You can easily imagine that such
subscripts would look ugly<br>
> array[scopedJavaScriptAt: 123] = ….<br>
><br>
> I propose to align the design of subscript with functions
where one could optionally give subscript<br>
> a name.<br>
><br>
> func name(label parameter: Type) -> ReturnType<br>
><br>
> subscript optionalName(label parameter: Type) ->
ReturnType<br>
> This change would make my API nice and<br>
> clean. array.scopedJavaScript[at: 213] = …<br>
<br>
You do that by giving your Array a scopedJavaScript property,
and<br>
making that indexable.<br>
<br>
--<br>
-Dave<br>
<br>
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</span></div>
</div>
</blockquote>
</div>
</div>
</div>
<div class="gmail-m_-4091591652219577513m_-7333948024739528437bloop_markdown">
</div>
</div>
<br>
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<br></blockquote>
</div>
<br></div>
</div>
</div>
</div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>