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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>I’ve got one more question that bothers me.</p>
<p>Lets say I’ve got a <code>class</code> that might look something like this:</p>
<pre><code class="swift">class Reference {
var pointer: UnsafeMutablePointer<Int>
init(integer: Int) {
self.pointer = UnsafeMutablePointer<Int>.alloc(1)
self.pointer.initialize(integer)
}
deinit {
self.pointer.destroy(1)
self.pointer.dealloc(1)
}
}
</code></pre>
<p>Let talk about ARC here. If I use optionals here and release manually the reference <code>deinit</code> will be called and we’re happy here:</p>
<pre><code class="swift">var reference: Reference? = Reference(integer: 123456789)
reference = nil
</code></pre>
<p>If I don’t use optionals because I want my value to exist while the application is running, <code>deinit</code> will never be called but my application terminates just fine (SIGKILL?):</p>
<pre><code class="swift">let reference = Reference(integer: 123456789)
</code></pre>
<ul>
<li><p>Doesn’t this create a memory leak?</p></li>
<li><p>How do I solve this problem, especially if don’t know whats inside the <code>Reference</code> type (assume I’m a different developer who only has access to the framework but not its implementation)?</p></li>
</ul>
<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_1464796999999258880" 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 23. Mai 2016 um 18:31:43, Jordan Rose (<a href="mailto:jordan_rose@apple.com">jordan_rose@apple.com</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class=""><div></div><div>
<title></title>
<br class="">
<div>
<blockquote type="cite" class="">
<div class="">On May 21, 2016, at 01:48, Adrian Zubarev via
swift-users <<a href="mailto:swift-users@swift.org" class="">swift-users@swift.org</a>> wrote:</div>
<br class="Apple-interchange-newline">
<div class="">
<div class="bloop_markdown" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; background-color: rgb(254, 254, 254);">
<p style="margin: 15px 0px; -webkit-margin-before: 0px;" class="">I
played around with<span class="Apple-converted-space"> </span><code style="font-family: Menlo, Consolas, 'Liberation Mono', Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(234, 234, 234); margin: 0px 2px; padding: 0px 5px; word-break: normal; word-wrap: normal; -webkit-margin-before: 0px;" class="">UnsafeMutablePointer</code><span class="Apple-converted-space"> </span>and realized one behavior:</p>
<pre style="margin: 15px 0px; font-family: Menlo, Consolas, 'Liberation Mono', Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(204, 204, 204); overflow: auto; padding: 4px 8px; word-break: normal; word-wrap: normal;" class=""><code class="swift" style="font-family: Menlo, Consolas, 'Liberation Mono', Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 0px; margin: 0px; padding: 0px; word-break: normal; word-wrap: normal; -webkit-margin-before: 0px;">let pString = UnsafeMutablePointer<String>.alloc(1)
pString.initialize("test")
pString.predecessor().memory // will crash ax expected
pString.predecessor() == pString.advancedBy(-1) // true
pString.destroy()
pString.dealloc(1)
</code>
</pre>
<p style="margin: 15px 0px;" class="">where</p>
<pre style="margin: 15px 0px; font-family: Menlo, Consolas, 'Liberation Mono', Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 1px solid rgb(204, 204, 204); overflow: auto; padding: 4px 8px; word-break: normal; word-wrap: normal;" class=""><code class="swift" style="font-family: Menlo, Consolas, 'Liberation Mono', Courier, monospace; font-size: 10pt; border-top-left-radius: 3px; border-top-right-radius: 3px; border-bottom-right-radius: 3px; border-bottom-left-radius: 3px; background-color: rgb(248, 248, 248); color: inherit; border: 0px; margin: 0px; padding: 0px; word-break: normal; word-wrap: normal; -webkit-margin-before: 0px;">let iInt = UnsafeMutablePointer<String>.alloc(1)
iInt.initialize("test")
iInt.predecessor().memory // will not crash
iInt.predecessor() == iInt.advancedBy(-1) // true
iInt.predecessor().memory = 42 // did I just modified some memory I don't own?
iInt.destroy()
iInt.dealloc(1)
</code>
</pre>
<p style="margin: 15px 0px;" class="">Is this intended? This is
really the case where its unsafe.</p>
</div>
</div>
</blockquote>
<br class=""></div>
<div>Dmitri’s answers are all better for this specific discussion,
but in general, “unsafe” in Swift means “if you don’t follow the
rules, this may crash, may silently corrupt memory or do other bad
things, may cause <i class="">other</i> code to be optimized
out or miscompiled, may be harmless”. In this particular case,
it’d be hard to check for the validity of the pointer while
<i class="">also</i> being fast and binary-compatible with
C.</div>
<div><br class=""></div>
<div>Jordan</div>
<br class="">
</div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>