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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 had a short conversation on Twitter with Joe Groff, here is what he said about it: “nowned/weak are meaningless inside a protocol”.</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_1494168047750948864" 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 7. Mai 2017 um 13:54:28, Greg Spiers 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>
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<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
Hello,</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
I hope this is the appropriate place to raise this discussion and
see if it's worth a proposal around which direction to take.</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
I've recently had some confusion around specifying weak for a
property in a protocol and surprised later of not being warned if
the adopting type does not also specify weak for the property.
There is an open bug around this behaviour [SR-479](<a href="https://bugs.swift.org/browse/SR-479">https://bugs.swift.org/browse/SR-479</a>).
Example:</p>
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class A {}</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
protocol P {</p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
weak var weakVar: A? { get set }</p>
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}</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
class B: P {</p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
var weakVar: A? // Not declared weak, no compiler
warning/error</p>
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}</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
Jordan Rose left the comment, "We need to figure out what weak
means in a protocol. We should probably ban it for now."</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
It is a little inconsistent to allow an ownership attribute in a
protocol but not enforce the same attribute in the adopting type I
think. I guess the point could be made that it's to document/hint
that the type adopting the protocol should use the ownership
attribute suggested? The Swift Programming Language reference has
this to say about Property Requirements in Protocols:</p>
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“A protocol can require any conforming type to provide an instance
property or type property with a particular name and type. The
protocol doesn’t specify whether the property should be a stored
property or a computed property—it only specifies the required
property name and type.”</p>
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<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
There’s no mention if the protocol can specify weak/unowned for a
property.</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
My concern is that this is a warning when this situation happens in
Objective-C and there's another bug that makes this point
[SR-1494](<a href="https://bugs.swift.org/browse/SR-1494">https://bugs.swift.org/browse/SR-1494</a>).</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
Would that be desirable behaviour to warn/error in Swift in the
adopting type? Or does it make more sense as Jordan commented on
the original bug to ban it in protocols (technically a source
breaking change)?</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
I've done some initial investigation on how difficult it would be
to [implement banning it in protocols](<a href="https://github.com/gspiers/swift/commit/ecde3ec5f61f259f8a396618e9973bac04536fd0">https://github.com/gspiers/swift/commit/ecde3ec5f61f259f8a396618e9973bac04536fd0</a>).
This would be my first contribution so sorry the code will need
some work but I'm happy to try and get it in shape and work on a
proposal if people think it's worth fixing.</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
Thanks,</p>
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<br></p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
</p>
<p style="margin:0px;font-size:12px;line-height:normal;font-family:'helvetica neue';color:rgb(69,69,69)">
Greg Spiers</p>
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