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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>You’re welcome. If you want to learn how <code>Metatypes</code> and <code>Existential Metatypes</code> work in Swift, take a look at our proposal where we discuss the current situation and how we want these types to be in Swift.</p>
<p><a href="https://github.com/DevAndArtist/swift-evolution/blob/cd9d8b3f1923d16f4381c23d3d335d88d83e32cd/proposals/0126-refactor-metatypes.md">Link</a></p>
<p>When learning about existential types, our proposal might be a little bit hard to follow. Feel free to ask.</p>
<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_1479757455270971904" 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 21. November 2016 um 20:42:12, Toni Suter (<a href="mailto:tonisuter@me.com">tonisuter@me.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>
Hi Adrian,
<div class=""><br class=""></div>
<div class="">Thanks for the link!</div>
<div class=""><br class=""></div>
<div class="">Best regards,</div>
<div class="">Toni</div>
<div class=""><br class=""></div>
<div class="">
<div>
<blockquote type="cite" class="">
<div class="">Am 21.11.2016 um 11:52 schrieb Adrian Zubarev
<<a href="mailto:adrian.zubarev@devandartist.com" class="">adrian.zubarev@devandartist.com</a>>:</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="">
Private message (I currently don’t have enough time to answer
everything):</p>
<p style="margin: 15px 0px;" class="">Take a look at his small
part:<span class="Apple-converted-space"> </span><a href="https://en.wikipedia.org/wiki/Type_system#Existential_types" style="color: rgb(65, 131, 196); background-color: inherit; text-decoration: none; -webkit-margin-before: 0px;" class="">https://en.wikipedia.org/wiki/Type_system#Existential_types</a></p>
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<br class="">
<div id="bloop_sign_1479725522992142080" class="bloop_sign">
<div style="font-family: helvetica, arial; font-size: 13px;" class="">-- <br class="">
Adrian Zubarev<br class="">
Sent with Airmail</div>
</div>
<br class="">
<p class="airmail_on" style="margin: 15px 0px;">Am 21. November
2016 um 11:09:43, Toni Suter via swift-users (<a href="mailto:swift-users@swift.org" style="color: rgb(65, 131, 196); background-color: inherit; text-decoration: none;" class="">swift-users@swift.org</a>) schrieb:</p>
<blockquote type="cite" class="clean_bq" style="margin: 15px 0px;">
<div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">
<div class=""></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">Hi everyone,</span>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><br class=""></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">I am trying to understand existentials in Swift. I
understand that in the</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">following code, P1 & P2 is an existential type,
because it supports values</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">from all types that conform to both P1 and
P2. </span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><br class=""></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">protocol P1 {}</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">protocol P2 {}</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">var x: P1 & P2</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><br class=""></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">However, this raises a few questions for me:</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><br class=""></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><b class="">1. In the following code, is x also an
existential?</b></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">protocol P {}</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">var x: P</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><br class=""></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">The proposals / blog posts that I read always talk about
the protocol composition syntax,</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">but to me, this is the same as the first example, just
with only a single protocol requirement.</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><br class=""></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><b class="">2. Are Any and AnyObject also
existentials?</b></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">So far, my understanding is:</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">Any is an existential with no requirements</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">AnyObject is an existential with only a class
requirement</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><b class=""><br class=""></b></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><b class="">3. Why can I not extend Any /
AnyObject?</b></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">For example, AnyObject is a protocol defined in the
standard library. Why is it not extensible?</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class=""><b class=""><br class=""></b></span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">Thanks and best regards,</span></div>
<div class=""><span style="margin-top: 0px; margin-bottom: 0px;" class="">Toni</span></div>
<span style="margin-top: 0px; margin-bottom: 0px;" class="">_______________________________________________<br class="">
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</span></div>
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