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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>This is the thread that I mentioned before: <a href="https://lists.swift.org/pipermail/swift-evolution/Week-of-Mon-20160502/016286.html">Should we rename “class” when referring to protocol conformance? </a></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_1477065599301243136" 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. Oktober 2016 um 17:12:37, Mike Kasianowicz via swift-evolution (<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>
<title></title>
<div dir="ltr">Just from an outside perspective, the class
restriction seems to be there as a kludge for technical reasons...
but that's neither here nor there.
<div><br></div>
<div>It is not so much to enforce a lack of identity - in the
struct case, it would be to enforce copy-by-value semantics.
I think the strongest argument I've got is, say, a serialization or
caching framework where you want to enforce that something is
entirely writeable via memory pointer or copyable. A
value-type restriction would get us mostly there, albeit there
would still be ways to break the contract. However, as noted
in my previous email, I see a lot of possibilities for enums too -
in that case the protocol somewhat acts as 'base type' without
adding the complexity of a base type.</div>
<div><br></div>
<div>I listed some of my examples in my previous email - I could
elaborate if it helps.<br></div>
</div>
<div class="gmail_extra"><br>
<div class="gmail_quote">On Fri, Oct 21, 2016 at 9:51 AM, Karl
Wagner <span dir="ltr"><<a href="mailto:razielim@gmail.com" target="_blank">razielim@gmail.com</a>></span> wrote:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div>
<div id="m_-3655154836993588012edo-message">
<div>IIRC, the reason we have "class" there is for the optimiser,
so it can optimise for the protocol being satisfied by a
reference-counted type. Classes are semantically unique from values
because they have identity, which is also something a protocol
might want to codify.</div>
<div><br></div>
<div>There may be some optimisation gains by requiring all
conformers to be values, but <span>I struggle to think of why
you might want to codify that a conformer should not have
identity.</span></div>
<div><span><br></span></div>
<div>Personally I don't really like this asymmetry in the language
either, and would support changes to make these two elements more
explicit. For example, a magic "hasIdentity" protocol which is
automatically satisfied only by classes, and moving the
optimisation guides to usage site (e.g. when declaring a variable
of type MyProto, I could declare it of type AnyClass<MyProto>
or AnyValue<MyProto> instead, to annotate this specific
instance as being refcountable or not, without making such
optimisation hints part of the MyProto definition)</div>
<div>
<div id="m_-3655154836993588012edo-signature" style="font-family:'Helvetica Neue','Helvetica',Helvetica,Arial,sans-serif;font:'-apple-system-body'">
</div>
<span class="HOEnZb"><font color="#888888"><br></font></span>
<div id="m_-3655154836993588012edo-link"></div>
</div>
<div><span class="HOEnZb"><font color="#888888">-
Karl</font></span></div>
</div>
<div id="m_-3655154836993588012edo-original">
<div><br>
<br>
<blockquote type="cite" style="margin:1ex 0 0 0;border-left:1px #ccc solid;padding-left:0.5ex">
<div>
<div class="h5">
<div>On Oct 21, 2016 at 8:39 am, <<a href="mailto:swift-evolution@swift.org" target="_blank">Mike Kasianowicz
via swift-evolution</a>> wrote:<br>
<br></div>
</div>
</div>
<div>
<div>
<div class="h5">
<div dir="ltr">Currently protocols can have the class constraint:
<div>protocol MyProtocol : class {}<br></div>
<div><br></div>
<div>It would be (a) intuitive and (b) useful to allow such things
as:</div>
<div>protocol Model : struct {} or protocol Event : enum {}</div>
<div><br></div>
<div>These types of restrictions can help prevent accidental
anti-patterns or misuse of APIs.</div>
<div><br></div>
<div>Seems simple and non-controversial... right?</div>
<div><br></div>
<div>[Note: I'd like to see even more heavy-handed protocol
restrictions in the future. For example, a protocol
describing an enum with a common case, or a struct with no
reference members. Great stuff for defensively coding APIs.]</div>
</div>
</div>
</div>
<span class="">______________________________<wbr>_________________
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</blockquote>
</div>
</div>
</div>
</blockquote>
</div>
<br></div>
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