<html><head><style>body{font-family:Helvetica,Arial;font-size:13px}</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><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> Hi Matthew thank you for remembering us about that draft. I’ll re-read it soon. At the a quick glance I noticed the extent use of the `where` clause. Wouldn’t make sense to simplify the main proposal and just focus on the `where` clause for typealises only? It’s already a complex feature on its own. Permitting the `where` clause in different places can sill be added later in the future.<br> <div id="bloop_sign_1503329141662461952" class="bloop_sign"></div> <br><p class="airmail_on">Am 21. August 2017 um 15:10:34, Matthew Johnson (<a href="mailto:matthew@anandabits.com">matthew@anandabits.com</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div dir="auto"><div></div><div>
<title></title>
<div><span style="background-color: rgba(255, 255, 255, 0);">If
anyone is thinking about spending time on this topic I recommend
beginning by reviewing the prior work that was done by Austin
Zheng. He has a proposal draft for enhanced existential that
is very thorough. Even if you're not planning to propose
everything that's included in his draft it would be a good idea to
be familiar with it. Here's the link: <a href="https://github.com/austinzheng/swift-evolution/blob/az-existentials/proposals/XXXX-enhanced-existentials.md">https://github.com/austinzheng/swift-evolution/blob/az-existentials/proposals/XXXX-enhanced-existentials.md</a>.<br>
</span><br>
Sent from my iPad</div>
<div><br>
On Aug 21, 2017, at 6:36 AM, Adrian Zubarev via swift-evolution
<<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>>
wrote:<br>
<br></div>
<blockquote type="cite">
<div>
<div class="bloop_markdown">
<p>It’s part of Generalized Existentials, but does not make it
complete. I think it would be worth adding more and more
functionality to existentials every year. We started first with
reshaping the syntax. This year we added support for classes. I
think next year would be good to have <code>where</code> clause
support for typealiases.</p>
<p>I understand the complexity of that particular feature, and it’s
a no-go for me to help on the implementation, but I’m willing to
drive the discussion and the proposal forward with other
co-authors. :)</p>
<p>Hasn’t it been said that the implementation must be at least a
*proof-of-concept* if the complexity is very high?</p>
<p>And my second question is: Wouldn’t the existence of this
feature reshape some parts of the standard library, isn’t that
affecting some major goals of Swift 5?</p>
<p>It would be nice if someone from the core team can clarify if
the <code>where</code> clause is out of scope for Swift 5 or
not.</p>
</div>
<div class="bloop_original_html">
<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_1503314850459755776" class="bloop_sign"></div>
<br>
<p class="airmail_on">Am 21. August 2017 um 12:51:48, David Hart
(<a href="mailto:david@hartbit.com">david@hartbit.com</a>)
schrieb:</p>
<blockquote type="cite" class="clean_bq">
<div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">
<div><span><br class=""></span>
<div>
<blockquote type="cite" class="">
<div class=""><span>On 21 Aug 2017, at 11:41, Adrian Zubarev
<<a href="mailto:adrian.zubarev@devandartist.com" class="">adrian.zubarev@devandartist.com</a>> wrote:</span></div>
<span><br class="Apple-interchange-newline"></span>
<div class="">
<div id="bloop_customfont" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px; margin: 0px;" class=""><span>Yes, `where` clause is welcome to typealises
(including generic ones) and existentials in general. I would love
to help on such proposal. I think David Hart is also interested in
this one. (cc)</span></div>
</div>
</blockquote>
<div><span><br class=""></span></div>
<div><span>Yes, this basically seems like <b class="">Generalized
Existentials</b> to me and is mentioned in the <a href="https://github.com/apple/swift/blob/master/docs/GenericsManifesto.md" class="">Generics Manifesto</a>. It’s a feature I hold very dear
but:</span></div>
<div><span><br class=""></span></div>
<div>
<ul class="MailOutline">
<li class=""><span>It’s a very difficult feature to implement and I
think Doug Gregor is the only/best person to do it</span></li>
<li class=""><span>I think its pretty much out of scope for Swift 5
(it’s not required for ABI Stability)</span></li>
</ul>
<div class=""><span><br class=""></span></div>
<div class=""><span>As a result, I’d be very surprised if this
topic got any discussion or implementation time during the Swift 5
timeframe.</span></div>
</div>
<blockquote type="cite" class="">
<div class="">
<p class="airmail_on" style="font-family: Helvetica, Arial; font-size: 13px; font-style: normal; font-variant-caps: normal; font-weight: normal; letter-spacing: normal; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; word-spacing: 0px; -webkit-text-stroke-width: 0px;">
<span>Am 21. August 2017 um 11:38:14, Gor Gyolchanyan via
swift-evolution (<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>) schrieb:</span></p>
<blockquote type="cite" class="clean_bq" 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-size-adjust: auto; -webkit-text-stroke-width: 0px;">
<div class="" style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;">
<div class=""></div>
<div class=""><span><span class="">Hello, Swift
community!</span></span>
<div class=""><span class=""><br class=""></span></div>
<div class=""><span class="">I'd like to start a discussion about a
possibility of constrained protocol aliases. The declaration would
look like this:</span></div>
<div class=""><span class=""><br class=""></span></div>
<div class="">
<div class=""><span class=""><font face="Menlo" class=""><font color="#941751" class="">typealias</font><span class="Apple-converted-space"> </span><font color="#008F00" class="">BinaryProtocol</font><span class="Apple-converted-space"> </span>=<span class="Apple-converted-space"> </span><font color="#008F00" class="">RandomAccessCollection</font><span class="Apple-converted-space"> </span>&<span class="Apple-converted-space"> </span><font color="#008F00" class="">MutablCollection</font><span class="Apple-converted-space"> </span>&<span class="Apple-converted-space"> </span><font color="#008F00" class="">RangeReplaceableCollection</font><span class="Apple-converted-space"> </span><font color="#941751" class="">where</font> <font color="#008F00" class="">Binary</font>.<font color="#008F00" class="">Index</font><span class="Apple-converted-space"> </span>==<span class="Apple-converted-space"> </span><font color="#008F00" class="">Int</font>,<span class="Apple-converted-space"> </span><font color="#008F00" class="">Binary</font>.<font color="#008F00" class="">Element</font><span class="Apple-converted-space"> </span>==<span class="Apple-converted-space"> </span><font color="#008F00" class="">Bool</font></font></span></div>
</div>
<div class=""><br class=""></div>
<div class="">The syntax and semantics of this declaration are
exactly the same as an analogous<span class="Apple-converted-space"> </span><font color="#941751" face="Menlo" class="">associatedtype</font><span class="Apple-converted-space"> </span>declaration inside a
protocol.</div>
<div class="">In the example above, the type<span class="Apple-converted-space"> </span><font face="Menlo" color="#008F00" class="">BinaryProtocol</font> represents a logical
array of bits and is a generic-only protocol that is usable in any
context where an integer-indexed mutable range-replaceable
random-access collection is expected.</div>
<div class="">Now, it can be used in a very concise and elegant
way:</div>
<div class=""><br class=""></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">public</font><span class="Apple-converted-space"> </span><font color="#941751" class="">protocol</font><span class="Apple-converted-space"> </span><font color="#008F00" class="">BinaryInitializable</font><span class="Apple-converted-space"> </span>{</font></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">init</font><<font color="#008F00" class="">Binary</font>>(binary:<span class="Apple-converted-space"> </span><font color="#008F00" class="">Binary</font>)<span class="Apple-converted-space"> </span><font color="#941751" class="">where</font><span class="Apple-converted-space"> </span><font color="#008F00" class="">Binary</font>:<span class="Apple-converted-space"> </span><font color="#008F00" class="">BinaryProtocol</font></font></div>
<div class=""><font face="Menlo" class="">}</font></div>
<div class=""><br class=""></div>
<div class="">which would otherwise look very verbose and
inelegant:</div>
<div class=""><br class=""></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">public</font><span class="Apple-converted-space"> </span><font color="#941751" class="">protocol</font><span class="Apple-converted-space"> </span><font color="#008F00" class="">BinaryInitializable</font><span class="Apple-converted-space"> </span>{</font></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">init</font><<font color="#008F00" class="">Binary</font>>(binary:<span class="Apple-converted-space"> </span><font color="#008F00" class="">Binary</font>)<span class="Apple-converted-space"> </span><font color="#941751" class="">where</font><span class="Apple-converted-space"> </span>Binary: <font color="#008F00" class="">RandomAccessCollection</font> & <font color="#008F00" class="">MutablCollection</font> & <font color="#008F00" class="">RangeReplaceableCollection,</font> <font color="#008F00" class="">Binary</font>.<font color="#008F00" class="">Index</font> == <font color="#008F00" class="">Int</font>, <font color="#008F00" class="">Binary</font>.<font color="#008F00" class="">Element</font> == <font color="#008F00" class="">Bool</font></font></div>
<div class=""><font face="Menlo" class="">}</font></div>
<div class="">
<div class=""><br class=""></div>
<div class="">Considering that smaller sets of constraints could be
aliased to their own protocol and then composited into more complex
aliases, this feature would dramatically improve readability and
maintainability of code that uses complex constraints, that
currently leads to arcane mess:</div>
<div class=""><br class=""></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">struct</font> <font color="#008F00" class="">Mirror</font> {</font></div>
<div class="">
<ul class="container" style="box-sizing: border-box; margin: 0px; padding: 0px; width: auto; list-style: none;">
<li class=""><font face="Menlo" class=""><font color="#797979" class="">/// ...</font></font></li>
<li class=""><font face="Menlo" class=""><font color="#941751" class="">init</font><<font color="#008F00" class="">Subject</font>, <font color="#008F00" class="">C</font> <font color="#941751" class="">where</font> <font color="#008F00" class="">C</font> : <font color="#008F00" class="">Collection</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Indices</font> : <font color="#008F00" class="">Collection</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font> : <font color="#008F00" class="">Collection</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Indices</font>.<font color="#008F00" class="">Index</font> == <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Index</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Indices</font>.<font color="#008F00" class="">SubSequence</font> == <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Indices</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Iterator</font>.<font color="#008F00" class="">Element</font> == <font color="#008F00" class="">Mirror</font>.<font color="#008F00" class="">Child</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font>.<font color="#008F00" class="">Index</font> == <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Index</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font>.<font color="#008F00" class="">Indices</font> : <font color="#008F00" class="">Collection</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font>.<font color="#008F00" class="">SubSequence</font> == <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Indices</font>.<font color="#008F00" class="">Iterator</font>.<font color="#008F00" class="">Element</font> == <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Index</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font>.<font color="#008F00" class="">Indices</font>.<font color="#008F00" class="">Index</font> == <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Index</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font>.<font color="#008F00" class="">Indices</font>.<font color="#008F00" class="">SubSequence</font> == <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font>.<font color="#008F00" class="">Indices</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font>.<font color="#008F00" class="">Iterator</font>.<font color="#008F00" class="">Element</font> == <font color="#008F00" class="">Mirror</font>.<font color="#008F00" class="">Child</font>, <font color="#008F00" class="">C</font>.<font color="#008F00" class="">SubSequence</font>.<font color="#008F00" class="">Indices</font>.<font color="#008F00" class="">Iterator</font>.<font color="#008F00" class="">Element</font> == <font color="#008F00" class="">C</font>.<font color="#008F00" class="">Index</font>>(_
subject: <font color="#008F00" class="">Subject</font>,
children: <font color="#008F00" class="">C</font>,
displayStyle: <font color="#008F00" class="">Mirror</font>.<font color="#008F00" class="">DisplayStyle</font>? = <font color="#941751" class="">default</font>, ancestorRepresentation: <font color="#008F00" class="">Mirror</font>.<font color="#008F00" class="">AncestorRepresentation</font> = <font color="#941751" class="">default</font>)</font></li>
</ul>
<div class=""><font face="Menlo" color="#797979" class="">///
...</font></div>
</div>
<div class=""><font face="Menlo" class="">}</font></div>
</div>
<div class=""><font face="Menlo" class=""><br class=""></font></div>
<div class=""><span class="" style="font-family: Menlo;"><br class=""></span></div>
<div class=""><font color="#797979" face="Menlo" class="">/// A
collection that is its own sub-sequence</font></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">typealias</font><span class="Apple-converted-space"> </span><font color="#008F00" class="">RecursivelySliceableCollection</font><span class="Apple-converted-space"> </span>=<span class="Apple-converted-space"> </span><font color="#008F00" class="">Collection</font><span class="Apple-converted-space"> </span><font color="#941751" class="">where</font></font></div>
<div class=""><font color="#008F00" face="Menlo" class="">RecursivelySliceableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">SubSequence</font><font face="Menlo" class="">:<span class="Apple-converted-space"> </span><font color="#008F00" class="">Collection</font>,</font></div>
<div class=""><font color="#008F00" face="Menlo" class="">RecursivelySliceableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">SubSequence</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Element</font><span class="Apple-converted-space"> </span><span class="" style="font-family: Menlo;">== </span><font color="#008F00" face="Menlo" class="">RecursivelySliceableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Element</font></div>
<div class=""><font color="#008F00" face="Menlo" class="">RecursivelySliceableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">SubSequence</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Indices</font><span class="Apple-converted-space"> </span><span class="" style="font-family: Menlo;">== </span><font color="#008F00" face="Menlo" class="">RecursivelySliceableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Indices</font><span class="" style="font-family: Menlo;">,</span></div>
<div class=""><font color="#008F00" face="Menlo" class="">RecursivelySliceableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">SubSequence</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">SubSequence</font><span class="Apple-converted-space"> </span><span class="" style="font-family: Menlo;">== </span><font color="#008F00" face="Menlo" class="">RecursivelySliceableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">SubSequence</font></div>
<div class=""><font face="Menlo" class=""><br class=""></font></div>
<div class=""><font color="#797979" face="Menlo" class="">/// A
collection that is its own index collection</font></div>
<div class=""><font color="#941751" face="Menlo" class="">typealias</font><span class="Apple-converted-space"> </span><font color="#008F00" face="Menlo" class="">RecursivelyIndexableCollection</font><span class="Apple-converted-space"> </span><span class="" style="font-family: Menlo;">=</span><span class="Apple-converted-space"> </span><font color="#008F00" face="Menlo" class="">Collection</font><span class="Apple-converted-space"> </span><font color="#941751" face="Menlo" class="">where</font></div>
<div class=""><font color="#008F00" face="Menlo" class="">RecursivelyIndexableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Indices</font><span class="Apple-converted-space"> </span><span class="" style="font-family: Menlo;">== </span><font color="#008F00" face="Menlo" class="">RecursivelySliceableCollection</font><span class="" style="font-family: Menlo;">,</span></div>
<div class=""><font color="#008F00" face="Menlo" class="">RecursivelyIndexableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Indices</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Index</font><span class="Apple-converted-space"> </span><span class="" style="font-family: Menlo;">== </span><font color="#008F00" face="Menlo" class="">RecursivelyIndexableCollection</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Index</font><span class="" style="font-family: Menlo;">,</span></div>
<div class=""><span class="" style="font-family: Menlo;"><br class=""></span></div>
<div class=""><font color="#941751" face="Menlo" class="">struct</font><span class="Apple-converted-space"> </span><span class="" style="font-family: Menlo;">Mirror {</span></div>
<div class=""><font color="#797979" face="Menlo" class="">///
...</font></div>
<div class=""><font color="#941751" face="Menlo" class="">init</font><span class="" style="font-family: Menlo;"><</span><font color="#008F00" face="Menlo" class="">Subject</font><span class="" style="font-family: Menlo;">,</span><span class="Apple-converted-space"> </span><font color="#008F00" face="Menlo" class="">C</font><span class="" style="font-family: Menlo;">: </span><font color="#008F00" face="Menlo" class="">RecursivelySliceableCollection</font><span class="Apple-converted-space"> </span><span class="" style="font-family: Menlo;">& </span><font color="#008F00" face="Menlo" class="">RecursivelyIndexableCollection</font><span class="" style="font-family: Menlo;">, </span><font color="#941751" face="Menlo" class="">where</font> <font color="#008F00" face="Menlo" class="">C</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Element</font><span class="Apple-converted-space"> </span><span class="" style="font-family: Menlo;">==</span><span class="Apple-converted-space"> </span><font color="#008F00" face="Menlo" class="">Mirror</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" face="Menlo" class="">Child</font><span class="" style="font-family: Menlo;">>(</span><span class="" style="font-family: Menlo;">_ subject:</span><span class="" style="font-family: Menlo;"> </span><font color="#008F00" class="" style="font-family: Menlo;">Subject</font><span class="" style="font-family: Menlo;">, children:</span><span class="" style="font-family: Menlo;"> </span><font color="#008F00" class="" style="font-family: Menlo;">C</font><span class="" style="font-family: Menlo;">, displayStyle:</span><span class="" style="font-family: Menlo;"> </span><font color="#008F00" class="" style="font-family: Menlo;">Mirror</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" class="" style="font-family: Menlo;">DisplayStyle</font><span class="" style="font-family: Menlo;">? =</span><span class="" style="font-family: Menlo;"> </span><font color="#941751" class="" style="font-family: Menlo;">default</font><span class="" style="font-family: Menlo;">, ancestorRepresentation:</span><span class="" style="font-family: Menlo;"> </span><font color="#008F00" class="" style="font-family: Menlo;">Mirror</font><span class="" style="font-family: Menlo;">.</span><font color="#008F00" class="" style="font-family: Menlo;">AncestorRepresentation</font><span class="" style="font-family: Menlo;"> </span><span class="" style="font-family: Menlo;">=</span><span class="" style="font-family: Menlo;"> </span><font color="#941751" class="" style="font-family: Menlo;">default</font><span class="" style="font-family: Menlo;">)</span></div>
<div class=""><font color="#797979" face="Menlo" class="">///
...</font></div>
<div class=""><span class="" style="font-family: Menlo;">}</span></div>
<div class=""><br class=""></div>
<div class="">Even considering that the proposal SE-0157 (<a href="https://github.com/apple/swift-evolution/blob/master/proposals/0157-recursive-protocol-constraints.md" class="">https://github.com/apple/swift-evolution/blob/master/proposals/0157-recursive-protocol-constraints.md</a>)
is going to make this specific use case a non-issue, the principle
applies to all cases where there are commonly used complex
constraints that don't necessarily involve recursive
constraints.</div>
<div class=""><br class=""></div>
<div class=""><b class="">Specializing Generic-Only Protocols For
Non-Generic Use</b></div>
<div class=""><br class=""></div>
<div class="">An additional feature that would prove to be very
useful would be to make a constrained protocol alias be a
non-generic-only protocol if the constraints of the alias
declaration specify a same-type requirement for all its associated
types, while defaulted associated types would also count.</div>
<div class="">Example:</div>
<div class=""><br class=""></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">protocol</font><span class="Apple-converted-space"> </span><font color="#008F00" class="">Consumer</font><span class="Apple-converted-space"> </span>{</font></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">associatedtype</font><span class="Apple-converted-space"> </span><font color="#008F00" class="">Consumable</font></font></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">mutating</font> <font color="#941751" class="">func</font><span class="Apple-converted-space"> </span>consume(_
consumable:<span class="Apple-converted-space"> </span><font color="#008F00" class="">Consumable</font>)<span class="Apple-converted-space"> </span><font color="#941751" class="">throws</font></font></div>
<div class=""><font face="Menlo" class="">}</font></div>
<div class=""><font face="Menlo" class=""><br class=""></font></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">var</font><span class="Apple-converted-space"> </span>consumer0:<span class="Apple-converted-space"> </span><font color="#008F00" class="">Consumer</font><span class="Apple-converted-space"> </span><font color="#797979" class="">// </font></font><span class="" style="font-family: Menlo;"><i class=""><font color="#FF2600" class="">error: Consumer is only usable in a generic
context</font></i></span></div>
<div class=""><font face="Menlo" class=""><br class=""></font></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">typealias</font><span class="Apple-converted-space"> </span><font color="#008F00" class="">CharacterConsumer</font><span class="Apple-converted-space"> </span>=<span class="Apple-converted-space"> </span><font color="#008F00" class="">Consumer</font><span class="Apple-converted-space"> </span><font color="#941751" class="">where </font> </font><span class="" style="color: rgb(0, 143, 0); font-family: Menlo;">Character</span><font face="Menlo" class=""><font color="#008F00" class="">Consumer</font>.<font color="#008F00" class="">Consumable</font><span class="Apple-converted-space"> </span>== </font><span class="" style="color: rgb(0, 143, 0); font-family: Menlo;">Character</span></div>
<div class=""><font face="Menlo" class=""><br class=""></font></div>
<div class=""><font face="Menlo" class=""><font color="#941751" class="">var</font><span class="Apple-converted-space"> </span>consumer1: </font><span class="" style="color: rgb(0, 143, 0); font-family: Menlo;">Character</span><font face="Menlo" class=""><font color="#008F00" class="">Consumer</font><span class="Apple-converted-space"> </span><font color="#797979" class="">// OK</font></font></div>
<div class=""><br class=""></div>
<div class="">The current workaround would be to declare a new
protocol with protocol inheritance clauses and a<span class="Apple-converted-space"> </span><font color="#941751" face="Menlo" class="">where</font><span class="Apple-converted-space"> </span>clause, but the major downside
is that it introduces a completely new protocol that is not
compatible with any context that expects the underlying protocols
and their constraints.</div>
<div class=""><br class=""></div>
<div class="">Regards,</div>
<div class="">Gor Gyolchanyan.</div>
<div class=""><br class=""></div>
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