<html><head><style>
body {
font-family: "Helvetica Neue", Helvetica, Arial, sans-serif;
padding:1em;
margin:auto;
background:#fefefe;
}
h1, h2, h3, h4, h5, h6 {
font-weight: bold;
}
h1 {
color: #000000;
font-size: 28pt;
}
h2 {
border-bottom: 1px solid #CCCCCC;
color: #000000;
font-size: 24px;
}
h3 {
font-size: 18px;
}
h4 {
font-size: 16px;
}
h5 {
font-size: 14px;
}
h6 {
color: #777777;
background-color: inherit;
font-size: 14px;
}
hr {
height: 0.2em;
border: 0;
color: #CCCCCC;
background-color: #CCCCCC;
display: inherit;
}
p, blockquote, ul, ol, dl, li, table, pre {
margin: 15px 0;
}
a, a:visited {
color: #4183C4;
background-color: inherit;
text-decoration: none;
}
#message {
border-radius: 6px;
border: 1px solid #ccc;
display:block;
width:100%;
height:60px;
margin:6px 0px;
}
button, #ws {
font-size: 12 pt;
padding: 4px 6px;
border-radius: 5px;
border: 1px solid #bbb;
background-color: #eee;
}
code, pre, #ws, #message {
font-family: Monaco;
font-size: 10pt;
border-radius: 3px;
background-color: #F8F8F8;
color: inherit;
}
code {
border: 1px solid #EAEAEA;
margin: 0 2px;
padding: 0 5px;
}
pre {
border: 1px solid #CCCCCC;
overflow: auto;
padding: 4px 8px;
}
pre > code {
border: 0;
margin: 0;
padding: 0;
}
#ws { background-color: #f8f8f8; }
.bloop_markdown table {
border-collapse: collapse;
font-family: Helvetica, arial, freesans, clean, sans-serif;
color: rgb(51, 51, 51);
font-size: 15px; line-height: 25px;
padding: 0; }
.bloop_markdown table tr {
border-top: 1px solid #cccccc;
background-color: white;
margin: 0;
padding: 0; }
.bloop_markdown table tr:nth-child(2n) {
background-color: #f8f8f8; }
.bloop_markdown table tr th {
font-weight: bold;
border: 1px solid #cccccc;
margin: 0;
padding: 6px 13px; }
.bloop_markdown table tr td {
border: 1px solid #cccccc;
margin: 0;
padding: 6px 13px; }
.bloop_markdown table tr th :first-child, table tr td :first-child {
margin-top: 0; }
.bloop_markdown table tr th :last-child, table tr td :last-child {
margin-bottom: 0; }
.bloop_markdown blockquote{
border-left: 4px solid #dddddd;
padding: 0 15px;
color: #777777; }
blockquote > :first-child {
margin-top: 0; }
blockquote > :last-child {
margin-bottom: 0; }
code, pre, #ws, #message {
word-break: normal;
word-wrap: normal;
}
hr {
display: inherit;
}
.bloop_markdown :first-child {
-webkit-margin-before: 0;
}
code, pre, #ws, #message {
font-family: Menlo, Consolas, Liberation Mono, Courier, monospace;
}
.send { color:#77bb77; }
.server { color:#7799bb; }
.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"><ul>
<li><p>If it’s possible to drop <code>T.Metatype</code>, sure why not to make it <code>Metatype<T></code>, but I have no idea hod the core team will build this. We should consider <code>typealias Metatype<T> = T.Metatype</code> as an alternative implementation, but tackle for <code>Metatype<T></code>.</p></li>
<li><p>Can you provide a full example?</p></li>
</ul>
<pre><code class="swift">let type = Type<Base>(casting: Derived)
// `type` is the same as this, where we know that `Derived` can be `Base`:
let derived = Type<Derived>()
let base = unsafeBitCast(derived, to: Type<Base>)
</code></pre>
<p>The global dictionary contains only the <code>dynamicTypes</code> which were instantiated through <code>Type<T>.sharedInstance</code> or <code>dynamicType(someInstance)</code> function.</p>
<pre><code class="swift">let derived: Any = Derived()
let type = dynamicType(derived) // Type<Any>
// I'll refer to current syntax here
type.metatype is Derived.Type // true
type.metatype is Base.Type // true
</code></pre>
<p>That example showed me that <code>public var metatype</code> need a fix:</p>
<pre><code class="swift">public var metatype: Metatype<T> {
// `_underlyingMetatype` is of type `T.Type` but stored in `Any.Type`
// we can sefely cast it back to `T.Type`
return unsafeBitCast(self._underlyingMetatype, to: Metatype<T>)
}
</code></pre>
<p>I just realized what causes the SR–2085 bug I mentioned earlier.</p>
<ul>
<li><code>Any.Type</code> is not the metatype of <code>Any</code></li>
<li><code>Any.Type</code> means that this ‘thing’ can store any metatype</li>
<li>There is no type that expresses metatype for <code>Any</code></li>
<li>We still can get the metatype for <code>Any</code> through <code>Any.self</code></li>
</ul>
<p>I updated SR–2085 and suggested that we need <code>AnyMetatype</code>.</p>
<p>I’ll update the implementation gist.</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_1468584985366941952" 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 15. Juli 2016 um 13:26:26, Anton Zhilin (<a href="mailto:antonyzhilin@gmail.com">antonyzhilin@gmail.com</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>
<title></title>
<div dir="ltr">OK, then, I guess, Swift can create type metainfo at
runtime, and it must work for <font face="monospace, monospace">Type<T></font>, as well. I'd
appreciate this feature.
<div><br></div>
<div>Next, I don't really like the following:<br>
<div>
<ul style="margin:15px 0px;font-size:12.8px">
<li style="margin:15px 0px">
<p style="margin:15px 0px">I’d rename <code style="font-family:Menlo,Consolas,"Liberation Mono",Courier,monospace;font-size:10pt;border-radius:3px;color:inherit;border:1px solid rgb(234,234,234);margin:0px 2px;padding:0px 5px;word-wrap:normal;background-color:rgb(248,248,248)">T.Type</code> to <code style="font-family:Menlo,Consolas,"Liberation Mono",Courier,monospace;font-size:10pt;border-radius:3px;color:inherit;border:1px solid rgb(234,234,234);margin:0px 2px;padding:0px 5px;word-wrap:normal;background-color:rgb(248,248,248)">T.Metatype</code> and
produce <code style="font-family:Menlo,Consolas,"Liberation Mono",Courier,monospace;font-size:10pt;border-radius:3px;color:inherit;border:1px solid rgb(234,234,234);margin:0px 2px;padding:0px 5px;word-wrap:normal;background-color:rgb(248,248,248)">typealias
Metatype<T> = T.Metatype</code></p>
</li>
<li style="margin:15px 0px">
<p style="margin:15px 0px">Furthermore <code style="font-family:Menlo,Consolas,"Liberation Mono",Courier,monospace;font-size:10pt;border-radius:3px;color:inherit;border:1px solid rgb(234,234,234);margin:0px 2px;padding:0px 5px;word-wrap:normal;background-color:rgb(248,248,248)">T.Metatype</code> would
be disallowed in declarations for the sake of <code style="font-family:Menlo,Consolas,"Liberation Mono",Courier,monospace;font-size:10pt;border-radius:3px;color:inherit;border:1px solid rgb(234,234,234);margin:0px 2px;padding:0px 5px;word-wrap:normal;background-color:rgb(248,248,248)">Metatype<T></code></p>
</li>
</ul>
<div>Why not remove <font face="monospace, monospace">T.Metatype</font> <font face="arial, helvetica, sans-serif">then</font>? <font face="monospace, monospace">Metatype<T></font> will be a
special data type that supports referring to static members of
<font face="monospace, monospace">T</font>.</div>
</div>
</div>
<div><br></div>
<div>Next, from "Bikeshedding". The global dictionary will only be
able to contain default-constructed <font face="monospace, monospace">Type<T></font> values, but not such as
<font face="monospace, monospace">Type<Base>(casting:
Derived.self)</font>. How do you deal with those?<br></div>
<div class="gmail_extra"><br>
<div class="gmail_quote">2016-07-15 13:47 GMT+03:00 Adrian Zubarev
via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span>:<br>
<blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">
<div style="word-wrap:break-word">
<div>
<p>Challenge accepted: Fixing your code to make it compile.</p>
<pre><code>typealias SomeGeneric<T> = (T, Int)
func wrap<T>(_ value: T) -> SomeGeneric<T> {
return (value, 42)
}
func recursivelyPrint<T>(_ value: T, depth: Int) {
print(value)
guard depth > 0 else { return }
recursivelyPrint(wrap(value), depth: depth - 1)
}
recursivelyPrint(2.0, depth: 5)
//////////// Output
2.0
(2.0, 42)
((2.0, 42), 42)
(((2.0, 42), 42), 42)
((((2.0, 42), 42), 42), 42)
(((((2.0, 42), 42), 42), 42), 42)
</code></pre>
<p>Technically <code>Type<T></code> should be able to reflect
other <code>Type<T></code>’s. There is nothing wrong about
it.</p>
<pre><code>let var1 = Int // Type: Type<Int>
let var2 = Int() // Type: Int
let var2 = Type<Int> // Type: Type<Type<Int>> where the metatype inside will be `Type<Int>.Type`
</code></pre>
<p>As you can see there won’t be any implicit infinite
recursion.</p>
</div>
<div>
<div style="font-family:Helvetica,Arial;font-size:13px;color:rgba(0,0,0,1.0);margin:0px;line-height:auto">
<span class=""><br></span></div>
<span class=""><br></span>
<div>
<div style="font-family:helvetica,arial;font-size:13px">
<span class="">-- <br>
Adrian Zubarev<br>
Sent with Airmail</span></div>
</div>
<span class=""><br></span>
<p><span class="">Am 15. Juli 2016 um 12:25:10, Adrian Zubarev
(<a href="mailto:adrian.zubarev@devandartist.com" target="_blank">adrian.zubarev@devandartist.com</a>) schrieb:</span></p>
<blockquote type="cite">
<div>
<blockquote style="font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span><span>> I don't see any problems with
Type<Type<T>>. There is finite number of types that are
used in the program, and compiler can collect and store information
about them all statically. Am I right?<br>
<br></span>Maybe not:<br>
<br>
<font face="monospace, monospace"> func
recursivelyPrint<T>(type: T.Type, depth: Int) {<br>
print(type)<br>
guard depth
> 0 else { return }<br>
recursivelyPrint(type: type.dynamicType, depth: depth - 1)<br>
}<br>
recursivelyPrint(type: Int.self, depth:
5)</font></span></blockquote>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<br></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class="">Great example. But we can adapt it to tuples or any
generic type:</span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class=""><br></span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class=""><font face="monospace, monospace">typealias
SomeGeneric<T> = (T, Int)</font></span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class=""><font face="monospace, monospace">func
wrap<T>(_ value: T) ->
SomeGeneric<T></font></span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class=""><font face="monospace, monospace"><br></font></span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<font face="monospace, monospace">func recursivelyPrint<T>(_
value: T, depth: Int) {</font></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class=""><font face="monospace, monospace">
print(type)</font></span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class=""><font face="monospace, monospace">
guard depth > 0 else { return }</font></span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class=""><font face="monospace, monospace">
recursivelyPrint(wrap(value), depth: delth - 1)</font></span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class=""><font face="monospace, monospace">}</font></span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class=""><br></span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
<span class="">Currently, such code does not compile, because
compiler can't create any types dynamically, not only
for<span> </span><font face="monospace, monospace">SomeGeneric<T> =
T.Type</font>.</span></div>
<div style="color:rgb(0,0,0);font-family:'helvetica Neue',helvetica;font-size:14px;font-style:normal;font-weight:normal;letter-spacing:normal;text-align:start;text-indent:0px;text-transform:none;white-space:normal;word-spacing:0px">
So this problem is not specific to Type<T>, and should not be
solved separately.</div>
</div>
</blockquote>
</div>
</div>
<br>
_______________________________________________<br>
swift-evolution mailing list<br>
<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a><br>
<a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br>
<br></blockquote>
</div>
<br></div>
</div>
</div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>