<div dir="ltr"><div class="gmail_extra">I like this much better ūüĎćūüŹľ.</div><div class="gmail_extra"><br></div><div class="gmail_extra">Although I think adding weak in there would make what&#39;s going on much clearer. [guard self] looks more like it returns if self is nil. [guard weak self] obviously has something to do with weak semantics.</div><div class="gmail_extra"><br></div><div class="gmail_extra"><br></div><div class="gmail_extra"><br><div class="gmail_quote">On Fri, Feb 12, 2016 at 10:44 AM, Erica Sadun via swift-evolution <span dir="ltr">&lt;<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div>So long as it&#39;s technically possible, this would rock.</div><span class="HOEnZb"><font color="#888888"><div><br></div><div>-- E</div></font></span><div><div class="h5"><div><br></div><br><div><blockquote type="cite"><div>On Feb 12, 2016, at 11:23 AM, Evan Maloney &lt;<a href="mailto:emaloney@gilt.com" target="_blank">emaloney@gilt.com</a>&gt; wrote:</div><br><div><div style="word-wrap:break-word"><div style="margin:0px;text-indent:6px;line-height:normal;font-family:&#39;Helvetica Neue&#39;"><div style="font-family:Courier;text-indent:0px">Hello,</div><div style="font-family:Courier;text-indent:0px"><br></div><div style="font-family:Courier;text-indent:0px">I sent out an earlier draft of this proposal last week, and have updated it based on feedback from the list.</div><div style="font-family:Courier;text-indent:0px"><br></div><div style="font-family:Courier;text-indent:0px">The newer proposal now has a much smaller conceptual footprint to address concerns that the previous iteration was too complex and would lead to verbose notation within the capture lists.</div><div style="font-family:Courier;text-indent:0px"><br></div><div style="font-family:Courier;text-indent:0px"><div>You can find the updated gist¬†<a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440" target="_blank">here</a>, as well as pasted below.</div></div><div style="font-family:Courier;text-indent:0px"><br></div><div style="font-family:Courier;text-indent:0px">Evan</div><div style="font-family:Courier;text-indent:0px"><br></div><div style="font-family:Courier;text-indent:0px">---</div><div style="font-family:Courier;text-indent:0px"><br></div><div style="font-family:Courier;text-indent:0px"><h1 style="font-size:2.25em;margin-right:0px;margin-bottom:16px;margin-left:0px;line-height:1.2;padding-bottom:0.3em;border-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,238,238);color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255);margin-top:0px!important">Simplified notation for avoiding the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:inherit;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">[weak self]</code>/<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:inherit;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">strongSelf</code>¬†dance with closures</h1><ul style="padding:0px 0px 0px 2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)"><li>Proposal: TBD</li><li>Author:¬†<a href="https://github.com/emaloney" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Evan Maloney</a></li><li>Status:¬†<strong>Draft</strong></li><li>Review manager: TBD</li></ul><h2 style="margin-top:1em;margin-bottom:16px;line-height:1.225;font-size:1.75em;padding-bottom:0.3em;border-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,238,238);color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#introduction" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Introduction</h2><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Frequently, closures are used as completion callbacks for asynchronous operations, such as when dealing with network requests. It is quite common to model these sorts of operations in such a way that an object instance represents a request/response transaction, for example:</p><div style="margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)"><pre style="overflow:auto;font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;margin-top:0px;margin-bottom:0px;line-height:1.45;padding:16px;background-color:rgb(247,247,247);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;word-wrap:normal;word-break:normal"><span style="color:rgb(167,29,93)">protocol</span> NetworkTransaction: <span style="color:rgb(167,29,93)">class</span>
{
    <span style="color:rgb(167,29,93)">enum</span> Result {
        <span style="color:rgb(167,29,93)">case</span> Succeeded(NSData)
        <span style="color:rgb(167,29,93)">case</span> Failed(<span style="color:rgb(0,134,179)">ErrorType</span>)
    }

    <span style="color:rgb(167,29,93)">func</span> <span style="color:rgb(121,93,163)">execute</span>(completion: (Result) <span style="color:rgb(167,29,93)">-&gt;</span> <span style="color:rgb(0,134,179)">Void</span>)
}</pre></div><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Here, the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">NetworkTransaction</code>¬†protocol declares the interface by which an asynchronous transaction occurs. The user of a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">NetworkTransaction</code>¬†calls the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">execute()</code>¬†function, passing in a completion function that is called at some time in the future, when the transaction completes.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">For example, imagine a hypothetical¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">DataConsumer</code>¬†class that uses a transaction to try to fetch some network data and process it:</p><div style="margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)"><pre style="overflow:auto;font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;margin-top:0px;margin-bottom:0px;line-height:1.45;padding:16px;background-color:rgb(247,247,247);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;word-wrap:normal;word-break:normal"><span style="color:rgb(167,29,93)">class</span> DataConsumer
{
    <span style="color:rgb(167,29,93)">let</span> transaction: NetworkTransaction

    <span style="color:rgb(167,29,93)">init</span>(transaction: NetworkTransaction)
    {
        <span style="color:rgb(167,29,93)">self</span><span style="color:rgb(167,29,93)">.</span>transaction <span style="color:rgb(167,29,93)">=</span> transaction
    }

    <span style="color:rgb(167,29,93)">func</span> <span style="color:rgb(121,93,163)">fetchData</span>()
    {
        transaction<span style="color:rgb(167,29,93)">.</span>execute() { [<span style="color:rgb(167,29,93)">weak</span> <span style="color:rgb(167,29,93)">self</span>] result <span style="color:rgb(167,29,93)">in</span>
            <span style="color:rgb(167,29,93)">guard</span> <span style="color:rgb(167,29,93)">let</span> strongSelf <span style="color:rgb(167,29,93)">=</span> <span style="color:rgb(167,29,93)">self</span> <span style="color:rgb(167,29,93)">else</span> { 
                <span style="color:rgb(167,29,93)">return</span>
            }

            <span style="color:rgb(167,29,93)">switch</span> result {
            <span style="color:rgb(167,29,93)">case</span> <span style="color:rgb(167,29,93)">.</span>Succeeded(<span style="color:rgb(167,29,93)">let</span> data):
                strongSelf<span style="color:rgb(167,29,93)">.</span>processData(data)

            <span style="color:rgb(167,29,93)">case</span> <span style="color:rgb(167,29,93)">.</span>Failed(<span style="color:rgb(167,29,93)">let</span> err):
                strongSelf<span style="color:rgb(167,29,93)">.</span>handleError(err)
            }
        }
    }

    <span style="color:rgb(167,29,93)">func</span> <span style="color:rgb(121,93,163)">processData</span>(data: NSData) 
    {
        <span style="color:rgb(150,152,150)">// process the data</span>
    }

    <span style="color:rgb(167,29,93)">func</span> <span style="color:rgb(121,93,163)">handleError</span>(error: <span style="color:rgb(0,134,179)">ErrorType</span>)
    {
        <span style="color:rgb(150,152,150)">// handle the error</span>
    }
}</pre></div><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">You&#39;ll notice the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">[weak self]</code>/<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">strongSelf</code>¬†dance in the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">fetchData()</code>¬†function. This is a common pattern with asynchronously-executed closures, and it signals the possibility that a closure might outlive its usefulness.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Because the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">NetworkTransaction</code>¬†may complete at any time, it is possible that the closure will execute after the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">DataConsumer</code>¬†that initiated the transaction has been deallocated. Perhaps the user has navigated elsewhere in the application and whatever data was to be fetched by¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">DataConsumer</code>¬†is no longer needed.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">In this case, after a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">DataConsumer</code>¬†instance goes away, we don&#39;t really want the closure doing anything. So, we capture¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†weakly to ensure that the closure doesn&#39;t hold a reference to the owning¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">DataConsumer</code>. That prevents a reference cycle and ensures that¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">DataConsumer</code>¬†can be deallocated when no longer in use.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">When it comes time to execute the closure, the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†statement effectively asks the question, &quot;Is¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†still alive?&quot; If the answer is no, the guard forces a return and the rest of the closure does not execute.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">If¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†<em>is</em>¬†still alive, then the weakly-captured¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†will be non-<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">nil</code>¬†and it will be converted into a strong reference held by¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">strongSelf</code>¬†for the duration of the closure&#39;s execution.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">When the closure is done executing,¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">strongSelf</code>¬†goes away, once again making the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">DataConsumer</code>¬†eligible for deallocation when no other references are held.</p><h2 style="margin-top:1em;margin-bottom:16px;line-height:1.225;font-size:1.75em;padding-bottom:0.3em;border-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,238,238);color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#the-problem" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>The Problem</h2><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">The¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">[weak self]</code>/<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">strongSelf</code>¬†dance requires common boilerplate wherever it is used, and the fact that a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>-like variable with an arbitrary name adds noise within the closure. The more¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">strongSelf</code>¬†is needed within the closure, the more noise there is.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Further, using a consistent name like¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">strongSelf</code>¬†is by convention only; it can&#39;t be enforced by the compiler, so searching your codebase for a given keyword won&#39;t be exhaustive if team members use the wrong name.</p><h2 style="margin-top:1em;margin-bottom:16px;line-height:1.225;font-size:1.75em;padding-bottom:0.3em;border-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,238,238);color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#proposed-solution" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Proposed Solution</h2><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">The proposed solution adds a new capture type by repurposing the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†keyword for another use, which would look like:</p><div style="margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)"><pre style="overflow:auto;font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;margin-top:0px;margin-bottom:0px;line-height:1.45;padding:16px;background-color:rgb(247,247,247);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;word-wrap:normal;word-break:normal">transaction<span style="color:rgb(167,29,93)">.</span>execute() { [<span style="color:rgb(167,29,93)">guard</span> <span style="color:rgb(167,29,93)">self</span>] result <span style="color:rgb(167,29,93)">in</span>
    <span style="color:rgb(167,29,93)">switch</span> result {
    <span style="color:rgb(167,29,93)">case</span> <span style="color:rgb(167,29,93)">.</span>Succeeded(<span style="color:rgb(167,29,93)">let</span> data):
        <span style="color:rgb(167,29,93)">self</span><span style="color:rgb(167,29,93)">.</span>processData(data)

    <span style="color:rgb(167,29,93)">case</span> <span style="color:rgb(167,29,93)">.</span>Failed(<span style="color:rgb(167,29,93)">let</span> err):
        <span style="color:rgb(167,29,93)">self</span><span style="color:rgb(167,29,93)">.</span>handleError(err)
    }
}</pre></div><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Here, the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">[guard self]</code>¬†capture list serves as a signal that the compiler should handle the weak/strong dance itself. When encountering¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">[guard self]</code>, the compiler should emit code that does the following:</p><ul style="padding:0px 0px 0px 2em;margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)"><li>Captures¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†in a weak reference on behalf of the closure</li><li>Whenever the closure is about to be executed, the weak reference is checked to see if¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†is still alive<ul style="padding:0px 0px 0px 2em;margin-top:0px;margin-bottom:0px"><li>If¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†is not alive, the closure becomes a¬†<a href="https://en.wikipedia.org/wiki/NOP" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">no-op</a>; calling the closure returns immediately without anything inside the braces being executed</li><li>If¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†is alive, it is upgraded to a strong reference for the lifetime of the closure&#39;s execution. Within the closure,¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†is non-optional, unlike how it would be with a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">[weak self]</code>¬†capture. When the closure is done executing, the strong reference will be cleared and only the weak reference will be held on behalf of the closure.</li></ul></li></ul><h3 style="margin-top:1em;margin-bottom:16px;line-height:1.43;font-size:1.5em;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#non-self-references" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1.2" target="_blank"><u></u><u></u><u></u><u></u></a>Non-<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:inherit;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†References</h3><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Because¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†is an additional capture type, like¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">weak</code>¬†and¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">unowned</code>, it can also be used to capture references other than¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>:</p><div style="margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)"><pre style="overflow:auto;font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;margin-top:0px;margin-bottom:0px;line-height:1.45;padding:16px;background-color:rgb(247,247,247);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;word-wrap:normal;word-break:normal"><span style="color:rgb(167,29,93)">let</span> capturingTwo <span style="color:rgb(167,29,93)">=</span> { [<span style="color:rgb(167,29,93)">guard</span> <span style="color:rgb(167,29,93)">self</span>, button] <span style="color:rgb(167,29,93)">in</span>
    <span style="color:rgb(150,152,150)">// weakly capture self and button</span>
    <span style="color:rgb(150,152,150)">// but execute the closure with strong references</span>
    <span style="color:rgb(150,152,150)">// if and only if self AND button still exist</span>
    <span style="color:rgb(150,152,150)">// when the closure is being asked to execute</span>
}</pre></div><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">When encountering multiple references being captured via¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>, the closure will execute¬†<strong>only</strong>¬†when¬†<em>all</em>¬†references are still alive when the closure is being asked to execute.</p><h3 style="margin-top:1em;margin-bottom:16px;line-height:1.43;font-size:1.5em;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#limitations" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1.2" target="_blank"><u></u><u></u><u></u><u></u></a>Limitations</h3><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Because¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†is a special capture type that causes the closure to become a no-op once a referenced object deallocates, it is only designed to be used with closures returning¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">Void</code>.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">This limitation was deemed acceptable because it would cover the vast majority of cases, and those that it didn&#39;t cover can still fall back on the existing technique.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">The compiler should emit an error if this notation is used in conjunction with a closure that has a non-<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">Void</code>¬†return type.</p><h2 style="margin-top:1em;margin-bottom:16px;line-height:1.225;font-size:1.75em;padding-bottom:0.3em;border-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,238,238);color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#caveats" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Caveats</h2><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">This notation is not intended to be a full-fledged replacement for guard statements within the closure. We are only using¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†here as a way to declare a specific memory-management behavior for references. Therefore,¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†within¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">[</code>square brackets¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">]</code>¬†should be seen as a capture type on par with¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">weak</code>¬†or¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">unowned</code>.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Unlike with a typical¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†statement, we are not attempting to support an¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">else</code>¬†or¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">where</code>¬†clause, or any boolean expressions within this notation.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Rather, we&#39;re simply adding a new capture behavior and providing a means to specify an early exit if the behavior couldn&#39;t be fulfilled because one or more objects was deallocated.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">The word¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†was chosen as the capture type because (1) it functions as a guard, ensuring that the closure doesn&#39;t execute unless the specified objects are still alive, and (2) it obviates the need for the full-fledged¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†statement that would otherwise be required to achieve the same result.</p><h2 style="margin-top:1em;margin-bottom:16px;line-height:1.225;font-size:1.75em;padding-bottom:0.3em;border-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,238,238);color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#impact-on-existing-code" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Impact on Existing Code</h2><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">None, since this does not affect any existing constructs. Implementation of this proposal will not result in any code breakage.</p><h2 style="margin-top:1em;margin-bottom:16px;line-height:1.225;font-size:1.75em;padding-bottom:0.3em;border-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,238,238);color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#alternatives-considered" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Alternatives Considered</h2><h3 style="margin-top:1em;margin-bottom:16px;line-height:1.43;font-size:1.5em;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#status-quo" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1.2" target="_blank"><u></u><u></u><u></u><u></u></a>Status Quo</h3><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">The primary alternative is to do nothing, requiring developers to add boilerplate guard code and handle upgrading the weak-to-strong references manually.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">As stated above, this leads to needless boilerplate that can easily be factored out by the compiler. Also, the use of a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>-like variable with an arbitrary name makes it more difficult to exhaustively find such uses in large projects. With this proposal, searching for the text &quot;<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">[guard</code>&quot; is all that&#39;s necessary to find all instances of this memory management technique.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Finally, the need to declare and use alternate names to capture values that already have existing names adds visual clutter to code and serves to obscure the code&#39;s original intent, making it harder to reason about.</p><h3 style="margin-top:1em;margin-bottom:16px;line-height:1.43;font-size:1.5em;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#closures-with-an-optional-return-type" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1.2" target="_blank"><u></u><u></u><u></u><u></u></a>Closures with an¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:inherit;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">Optional</code>¬†Return Type</h3><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">One possible addition to this proposal would extend support to any closure returning an¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">Optional</code>¬†of some kind.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">If one of the objects in a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†capture list has been deallocated, executing the closure will always result in an immediate¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">nil</code>¬†return.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">This idea was excluded from this iteration of the proposal due to a concern that it relied on a &quot;magic return value&quot; (albeit a reasonable one) and a perception that the community favored a solution with a smaller conceptual footprint.</p><h3 style="margin-top:1em;margin-bottom:16px;line-height:1.43;font-size:1.5em;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#closures-with-a-bool-return-type" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1.2" target="_blank"><u></u><u></u><u></u><u></u></a>Closures with a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:inherit;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">Bool</code>¬†Return Type</h3><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">One possible addition to this proposal would extend support to any closure returning a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">Bool</code>.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">If one of the objects in a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>¬†capture list has been deallocated, executing the closure will always result in an immediate¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">false</code>¬†return.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">This idea was excluded from this iteration of the proposal due to a concern that it relied on a &quot;magic return value&quot; (albeit a reasonable one) and a perception that the community favored a solution with a smaller conceptual footprint.</p><h3 style="margin-top:1em;margin-bottom:16px;line-height:1.43;font-size:1.5em;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#closures-with-arbitrary-return-types" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1.2" target="_blank"><u></u><u></u><u></u><u></u></a>Closures with Arbitrary Return Types</h3><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">An earlier iteration of this proposal included support for closures with arbitrary return values. The community consensus was that the proposal was too heavy-weight and tried to do too much, and would lead to verbosity within the capture declaration. As a result, this idea was removed from the proposal.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">The ability to handle non-<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">Void</code>¬†return values relied on supporting an¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">else</code>¬†clause within a¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard</code>-based capture list:</p><div style="margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)"><pre style="overflow:auto;font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;margin-top:0px;margin-bottom:0px;line-height:1.45;padding:16px;background-color:rgb(247,247,247);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px;word-wrap:normal;word-break:normal"><span style="color:rgb(167,29,93)">let</span> happinessLevel: () <span style="color:rgb(167,29,93)">-&gt;</span> <span style="color:rgb(0,134,179)">Int</span> <span style="color:rgb(167,29,93)">=</span> { [<span style="color:rgb(167,29,93)">guard</span> <span style="color:rgb(167,29,93)">self</span> <span style="color:rgb(167,29,93)">else</span> <span style="color:rgb(0,134,179)">-1</span>] <span style="color:rgb(167,29,93)">in</span>
    <span style="color:rgb(167,29,93)">var</span> level <span style="color:rgb(167,29,93)">=</span> <span style="color:rgb(0,134,179)">0</span>
    level <span style="color:rgb(167,29,93)">+=</span> <span style="color:rgb(167,29,93)">self</span><span style="color:rgb(167,29,93)">.</span>isHealthy <span style="color:rgb(167,29,93)">?</span> <span style="color:rgb(0,134,179)">25</span> <span style="color:rgb(167,29,93)">:</span> <span style="color:rgb(0,134,179)">0</span>
    level <span style="color:rgb(167,29,93)">+=</span> <span style="color:rgb(167,29,93)">!</span><span style="color:rgb(167,29,93)">self</span><span style="color:rgb(167,29,93)">.</span>isHungry <span style="color:rgb(167,29,93)">?</span> <span style="color:rgb(0,134,179)">25</span> <span style="color:rgb(167,29,93)">:</span> <span style="color:rgb(0,134,179)">0</span>
    level <span style="color:rgb(167,29,93)">+=</span> <span style="color:rgb(167,29,93)">!</span><span style="color:rgb(167,29,93)">self</span><span style="color:rgb(167,29,93)">.</span>isFearful <span style="color:rgb(167,29,93)">?</span> <span style="color:rgb(0,134,179)">25</span> <span style="color:rgb(167,29,93)">:</span> <span style="color:rgb(0,134,179)">0</span>
    level <span style="color:rgb(167,29,93)">+=</span> <span style="color:rgb(167,29,93)">self</span><span style="color:rgb(167,29,93)">.</span>hasLove <span style="color:rgb(167,29,93)">?</span> <span style="color:rgb(0,134,179)">25</span> <span style="color:rgb(167,29,93)">:</span> <span style="color:rgb(0,134,179)">0</span>
    <span style="color:rgb(167,29,93)">return</span> level
}</pre></div><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Here, the¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">else</code>¬†clause provides a value to return in cases where¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†has gone away and the guard fails.</p><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">In this example, if you call¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">happinessLevel()</code>¬†after¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">self</code>¬†has been deallocated, the value¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">-1</code>¬†will always be returned.</p><h2 style="margin-top:1em;margin-bottom:16px;line-height:1.225;font-size:1.75em;padding-bottom:0.3em;border-bottom-width:1px;border-bottom-style:solid;border-bottom-color:rgb(238,238,238);color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;background-color:rgb(255,255,255)"><a href="https://gist.github.com/emaloney/d34ac9b134ece7c60440#citations" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none;display:inline-block;padding-right:2px;line-height:1" target="_blank"><u></u><u></u><u></u><u></u></a>Citations</h2><p style="margin-top:0px;margin-bottom:16px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255)">Variations on this proposal were discussed earlier in the following¬†<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">swift-evolution</a>¬†threads:</p><ul style="padding:0px 0px 0px 2em;margin-top:0px;color:rgb(51,51,51);font-family:&#39;Helvetica Neue&#39;,Helvetica,&#39;Segoe UI&#39;,Arial,freesans,sans-serif,&#39;Apple Color Emoji&#39;,&#39;Segoe UI Emoji&#39;,&#39;Segoe UI Symbol&#39;;font-size:16px;background-color:rgb(255,255,255);margin-bottom:0px!important"><li><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160201/008713.html" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Wanted: syntactic sugar for [weak self] callbacks</a></li><li><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160201/009023.html" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">Allowing¬†<code style="font-family:Consolas,&#39;Liberation Mono&#39;,Menlo,Courier,monospace;font-size:14px;padding:0.2em 0px;margin:0px;background-color:rgba(0,0,0,0.0392157);border-top-left-radius:3px;border-top-right-radius:3px;border-bottom-right-radius:3px;border-bottom-left-radius:3px">guard let self = self else { ‚Ķ }</code>¬†for weakly captured self in a closure.</a></li><li><a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160201/009241.html" style="background-color:transparent;color:rgb(64,120,192);text-decoration:none" target="_blank">[Draft Proposal] A simplified notation for avoiding the weak/strong dance with closure capture lists</a></li></ul><div><br></div></div></div></div></div></blockquote></div><br></div></div></div><br>_______________________________________________<br>
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