Arrays are copy-on-write, and you don't need to allow the storage to be replaced if you don't want to, because the properties can be read-only. <br><div class="gmail_quote"><div dir="ltr">On Fri, Nov 18, 2016 at 02:34 Adrian Zubarev <<a href="mailto:adrian.zubarev@devandartist.com">adrian.zubarev@devandartist.com</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="gmail_msg"><div class="m_-8967909558215416107bloop_markdown gmail_msg"><p class="gmail_msg">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 class="gmail_msg">However the named subscript would allow me to mutate in-place. </p>
<p class="gmail_msg">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 class="gmail_msg"><code class="m_-8967909558215416107swift gmail_msg">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 class="gmail_msg"></p></div><div class="m_-8967909558215416107bloop_original_html gmail_msg"></div></div><div style="word-wrap:break-word" class="gmail_msg"><div class="m_-8967909558215416107bloop_original_html gmail_msg"><div id="m_-8967909558215416107bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto" class="gmail_msg"><br class="gmail_msg"></div> <br class="gmail_msg"> <div id="m_-8967909558215416107bloop_sign_1479457293736585984" class="m_-8967909558215416107bloop_sign gmail_msg"><div style="font-family:helvetica,arial;font-size:13px" class="gmail_msg">-- <br class="gmail_msg">Adrian Zubarev<br class="gmail_msg">Sent with Airmail</div></div> <br class="gmail_msg"></div></div><div style="word-wrap:break-word" class="gmail_msg"><div class="m_-8967909558215416107bloop_original_html gmail_msg"><p class="m_-8967909558215416107airmail_on gmail_msg">Am 18. November 2016 um 09:19:20, Xiaodi Wu (<a href="mailto:xiaodi.wu@gmail.com" class="gmail_msg" target="_blank">xiaodi.wu@gmail.com</a>) schrieb:</p> <blockquote type="cite" class="m_-8967909558215416107clean_bq gmail_msg"><span class="gmail_msg"><div class="gmail_msg"><div class="gmail_msg"></div><div class="gmail_msg">
<div dir="ltr" class="gmail_msg">I believe Dave had a design more like this in mind:
<div class="gmail_msg"><br class="gmail_msg"></div>
<div class="gmail_msg">```<br class="gmail_msg">
<div class="gmail_msg">
<div class="gmail_msg">struct _View<T> {</div>
<div class="gmail_msg"> let array: Array<Any></div>
<div class="gmail_msg"> subscript(index: Int) -> T? {</div>
<div class="gmail_msg"> guard index >= 0 &&
index < array.count else { return nil }</div>
<div class="gmail_msg"> return array[index] as? T</div>
<div class="gmail_msg"> }</div>
<div class="gmail_msg">}</div>
<div class="gmail_msg"><br class="gmail_msg"></div>
<div class="gmail_msg">extension Array {</div>
<div class="gmail_msg"> var double: _View<Double> {</div>
<div class="gmail_msg"> return _View(array: self)</div>
<div class="gmail_msg"> }</div>
<div class="gmail_msg">}</div>
</div>
<div class="gmail_msg">```</div>
<div class="gmail_extra gmail_msg"><br class="gmail_msg">
<div class="gmail_quote gmail_msg">On Fri, Nov 18, 2016 at 2:00 AM, Adrian
Zubarev via swift-evolution <span dir="ltr" class="gmail_msg"><<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br class="gmail_msg">
<blockquote class="gmail_quote gmail_msg" 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="gmail_msg">
<div class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437bloop_markdown gmail_msg">
<p class="gmail_msg">Hi Dave,</p>
<p class="gmail_msg">Thank you for your answer. I have to admit this is a
‘workaround’ but it will make everything even worse.</p>
<p class="gmail_msg">From:</p>
<pre class="gmail_msg"><code class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437swift gmail_msg">public func scopedJavaScript(at index: Int) -> (javaScript: String, scope: Document)?
</code></pre>
<p class="gmail_msg">To:</p>
<pre class="gmail_msg"><code class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437swift gmail_msg">public subscript(at index: Int) -> (javaScript: String, scope: Document)?
public var scopedJavaScript: Array {
get { return self }
set { /* implementation artifact */ }
}
</code></pre>
<p class="gmail_msg">Now I could write code like
<code class="gmail_msg">array.scopedJavaScript.scopedJavaScript.scopedJavaScript</code>
and so one, which makes no sense any more.</p>
<p class="gmail_msg">Where we could simply allow:</p>
<pre class="gmail_msg"><code class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437swift gmail_msg">public subscript scopedJavaScript(at index: Int) -> (javaScript: String, scope: Document)?
</code></pre>
<p class="gmail_msg">This would ensure that the user can only write something
like:</p>
<pre class="gmail_msg"><code class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437swift gmail_msg">array.scopedJavaScript[at: 42] // get the value
array.scopedJavaScript[at: 42] = (…, …) // set the value
</code></pre>
<ul class="gmail_msg">
<li class="gmail_msg">Is there anything that speaks against optionally named
subscripts?</li>
<li class="gmail_msg">Technical reasons?</li>
<li class="gmail_msg">Swiftiness?</li>
</ul>
</div>
<div class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437bloop_original_html gmail_msg">
<div id="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437bloop_customfont" style="font-family:helvetica,arial;font-size:13px;color:rgb(0,0,0);margin:0px" class="gmail_msg">
<span class="gmail_msg"><br class="gmail_msg"></span></div>
<span class="gmail_msg"><br class="gmail_msg"></span>
<div id="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437bloop_sign_1479455258346931968" class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437bloop_sign gmail_msg">
<div style="font-family:helvetica,arial;font-size:13px" class="gmail_msg">
<span class="gmail_msg">-- <br class="gmail_msg">
Adrian Zubarev<br class="gmail_msg">
Sent with Airmail</span></div>
</div>
<span class="gmail_msg"><br class="gmail_msg"></span>
<div class="gmail_msg">
<div class="m_-8967909558215416107gmail-m_-4091591652219577513h5 gmail_msg">
<p class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437airmail_on gmail_msg">Am
17. November 2016 um 23:33:44, Dave Abrahams via swift-evolution
(<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>) schrieb:</p>
<blockquote type="cite" class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437clean_bq gmail_msg">
<div class="gmail_msg">
<div class="gmail_msg"><span class="gmail_msg"><br class="gmail_msg">
on Thu Nov 17 2016, Adrian Zubarev <<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:<br class="gmail_msg">
<br class="gmail_msg">
> Dear Swift community,<br class="gmail_msg">
><br class="gmail_msg">
> while building a framework for BSON I had the following
idea.<br class="gmail_msg">
><br class="gmail_msg">
> Here is a snippet of some code I do have in my module:<br class="gmail_msg">
><br class="gmail_msg">
> extension Array where Element == Document.Value {<br class="gmail_msg">
><br class="gmail_msg">
> public func double(at index: Int) -> Double? {<br class="gmail_msg">
><br class="gmail_msg">
> guard self.startIndex <= index && index <
self.endIndex else { return nil }<br class="gmail_msg">
><br class="gmail_msg">
> if case .double(let double) = self[index] {<br class="gmail_msg">
><br class="gmail_msg">
> return double<br class="gmail_msg">
> }<br class="gmail_msg">
> return nil<br class="gmail_msg">
> }<br class="gmail_msg">
><br class="gmail_msg">
> …<br class="gmail_msg">
> }<br class="gmail_msg">
> This function is used to query the array and check if the
element at the given index is of a<br class="gmail_msg">
> specific type. Now I would like also to implement a
semi-schema setter.<br class="gmail_msg">
><br class="gmail_msg">
> The problem that I see, is the ugliness of the subscript I’d
create.<br class="gmail_msg">
><br class="gmail_msg">
> Currently the code would read nicely let d = array.double(at:
42), but after change to a subscript<br class="gmail_msg">
> the API would look odd array[doubleAt: 42] = 5.0.<br class="gmail_msg">
><br class="gmail_msg">
> Don’t get me wrong here, I also have methods with larger names
like public func scopedJavaScript(at<br class="gmail_msg">
> index: Int) -> …. You can easily imagine that such
subscripts would look ugly<br class="gmail_msg">
> array[scopedJavaScriptAt: 123] = ….<br class="gmail_msg">
><br class="gmail_msg">
> I propose to align the design of subscript with functions
where one could optionally give subscript<br class="gmail_msg">
> a name.<br class="gmail_msg">
><br class="gmail_msg">
> func name(label parameter: Type) -> ReturnType<br class="gmail_msg">
><br class="gmail_msg">
> subscript optionalName(label parameter: Type) ->
ReturnType<br class="gmail_msg">
> This change would make my API nice and<br class="gmail_msg">
> clean. array.scopedJavaScript[at: 213] = …<br class="gmail_msg">
<br class="gmail_msg">
You do that by giving your Array a scopedJavaScript property,
and<br class="gmail_msg">
making that indexable.<br class="gmail_msg">
<br class="gmail_msg">
--<br class="gmail_msg">
-Dave<br class="gmail_msg">
<br class="gmail_msg">
_______________________________________________<br class="gmail_msg">
swift-evolution mailing list<br class="gmail_msg">
<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a><br class="gmail_msg">
<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="gmail_msg" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class="gmail_msg">
</span></div>
</div>
</blockquote>
</div>
</div>
</div>
<div class="m_-8967909558215416107gmail-m_-4091591652219577513m_-7333948024739528437bloop_markdown gmail_msg">
</div>
</div>
<br class="gmail_msg">
_______________________________________________<br class="gmail_msg">
swift-evolution mailing list<br class="gmail_msg">
<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a><br class="gmail_msg">
<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" class="gmail_msg" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class="gmail_msg">
<br class="gmail_msg"></blockquote>
</div>
<br class="gmail_msg"></div>
</div>
</div>
</div></div></span></blockquote></div></div></blockquote></div>