<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"><p>As a naming contrast, one could make <code>Self</code> like the proposed <code>Current</code>, and rename the current <code>Self</code> to <code>DynamicSelf</code> or something similar.</p>
<p>Most protocols that are meant for value types in first place should use <code>Self</code> aka. <code>Current</code> as the return type.</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_1483785896037235968" 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. Januar 2017 um 11:38:55, Adrian Zubarev (<a href="mailto:adrian.zubarev@devandartist.com">adrian.zubarev@devandartist.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;"><div></div><div>
<title></title>
<div class="bloop_markdown">
<p>Hi Swift community,</p>
<p>I’d like to talk to about current <code>Self</code> keyword. If
I’m not totally mistaken then the current <code>Self</code> has a
few meanings:</p>
<ol>
<li>Refer to the <em>current</em> type, or refer to the dynamic
type for non-final classes inside containing type (SE–0068 - not
yet implemented).</li>
<li>For non-final class types use <code>Self</code> as return type
on the conforming super type (or <em>return an instance of receiver
<code>Self</code></em>).</li>
</ol>
<p>Let me visualize the behaviors quickly in some short code
snippet:</p>
<pre><code class="swift">protocol Foo {
func foo(_ f: Self) -> Self
}
class A : Foo {
// forced to use `A` as parameter type and `Self` as return type
func foo(_ f: A) -> Self { return self }
// Returning `A()` would cause an error: Cannot convert return expression of type 'A' to return type 'Self'
func bar() -> A { return A() /* or self */ }
func zoo() -> Self { return /* only */ self }
}
class B : A {
// Both is fine `B` or `Self` as the return type
// If `B` is used you can return a different instance like `B()`
// `Self` does only allow `self` to be used here
override func foo(_ f: A) -> B { return self }
}
struct D : Foo {
// No `Self` allowed here at all
func foo(_ f: D) -> D { return self /* or D() */ }
}
</code></pre>
<p>The behavior of <code>Self</code> is a little magical, because
it sometimes refers to the <em>current</em> type it is used in, or
it has a contract of using <code>self</code>.</p>
<hr>
<p>I propose of introducing a new keyword called
<code>Current</code> to solve a few problems here.</p>
<ol>
<li>
<p><code>Self</code> on parameter types would be disallowed for
protocol members, because conformances to that protocol already
disallow that (see <code>A</code> above). Instead one would use
<code>Current</code> and get the correct meaning.</p>
<pre><code class="swift">protocol Boo {
func boo(_ b: Current) -> Self
}
procotol Loo {
func loo() -> Current
}
class X : Boo, Loo {
func boo(_ b: X) -> Self { return self }
func loo() -> X { return self /* or X() */ }
}
final class Y : Boo {
func boo(_ b: X) -> Y { return self /* or Y */ }
}
</code></pre></li>
<li>
<p>Using <code>Self</code> inside the containing type would always
mean as one would refer to the dynamic type, like the magical
syntax function <code>type(of:)</code> does.</p>
</li>
<li>
<p><code>Current</code> can only refer to the current containing
type.</p>
</li>
<li>
<p>On classes <code>Self</code> has always the contract of
returning <code>self</code>.</p>
</li>
<li>
<p><code>Self</code> could be discouraged in favor of
<code>Current</code> on value types, as a shorthand to refer to the
containing type.</p>
</li>
<li>
<p>Generics could benefit from <code>Current</code> too:</p>
<pre><code class="swift">extension AReallyLongNonFinalClassName {
func casted<T : Current>() -> T { ... }
}
// `Self` wouldn't here, because it would refer to the dynamic type
</code></pre></li>
</ol>
<p>#1 Would affect a lot of protocols which implies that it would
affect ABI.</p>
<hr>
<p>These are the first ideas I had in my mind. We can polish it
further if it receives positive and constructive feedback.</p>
<p>Best regards,</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_1483779578617182976" class="bloop_sign">
<div style="font-family:helvetica,arial;font-size:13px">
-- <br>
Adrian Zubarev<br>
Sent with Airmail</div>
</div>
</div>
<div class="bloop_markdown"></div>
</div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>