<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; line-break: after-white-space;"><div class="bloop_markdown"><p>If I change it slightly </p>
<pre><code>protocol JSONDecodable { init() }
protocol CompressedDecodable: JSONDecodable { }
class NetworkRequest<T: JSONDecodable> {
var response: T?
func doAThing() {
response = doSomething()
}
func doSomething<T: JSONDecodable>() -> T {
print("One: \(T.self)")
return T()
}
}
class CompressedNetworkRequest<U: CompressedDecodable>: NetworkRequest<U> {
override func doSomething<U: CompressedDecodable>() -> U {
print("Two: \(U.self)")
return U()
}
}
struct Uno: JSONDecodable { }
struct Dos: CompressedDecodable { }
NetworkRequest<Uno>().doAThing()
CompressedNetworkRequest<Dos>().doAThing()
</code></pre>
<p>I do get the output:</p>
<pre><code>One: Uno
Two: Dos
</code></pre>
<p>But I also get a crash <code>error: Execution was interrupted, reason: EXC_BAD_ACCESS (code=EXC_I386_GPFLT).</code></p>
<p></p><p>—<br>
Fred</p>
<p></p></div><div class="bloop_original_html"><style>body{font-family:Helvetica,Arial;font-size:14px}</style><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:14px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;"><br></div> <br> <div class="bloop_sign" id="bloop_sign_1510820806587976960"></div> <div class="airmail_ext_on" style="color:black"><br>From: <span style="color:black">Jon Shier via swift-users</span> <a href="mailto:swift-users@swift.org"><swift-users@swift.org></a><br>Reply: <span style="color:black">Jon Shier</span> <a href="mailto:jon@jonshier.com"><jon@jonshier.com></a><br>Date: <span style="color:black">16 November 2017 at 05:43:06</span><br>To: <span style="color:black">Седых Александр via swift-users</span> <a href="mailto:swift-users@swift.org"><swift-users@swift.org></a><br>Subject: <span style="color:black"> [swift-users] Refining generics in classes <br></span></div><br> <blockquote type="cite" class="clean_bq"><span><div><div></div><div> Swift Users:<br> I have a generics use case which has somewhat stumped me. I have two related protocols, JSONDecodable and CompressedDecodable, and CompressedDecodable inherits from JSONDecodable (though that relationship isn’t strictly necessary). I also have a generic function that’s overloaded for each of those protocols. I’m trying to write a class to make a network request expecting a generic response type of either JSONDecodable or CompressedDecodable. However, it doesn’t seem possible to write it in such a way that the overload I need is called. Instead, it’s always the superclass’ type’s overload that is called. For example:<br><br>protocol JSONDecodable { init() }<br>protocol CompressedDecodable: JSONDecodable { }<br><br>class NetworkRequest<T: JSONDecodable> {<br> <br> var response: T?<br> <br> func doAThing() {<br> response = doSomething()<br> }<br>}<br><br>class CompressedNetworkRequest<U: CompressedDecodable>: NetworkRequest<U> {<br> <br>}<br><br>func doSomething<T: JSONDecodable>() -> T {<br> print("One: \(T.self)")<br> return T()<br>}<br><br>func doSomething<T: CompressedDecodable>() -> T {<br> print("Two: \(T.self)")<br> return T()<br>}<br><br>struct Uno: JSONDecodable { }<br>struct Dos: CompressedDecodable { }<br><br>NetworkRequest<Uno>().doAThing()<br>CompressedNetworkRequest<Dos>().doAThing()<br><br>In a playground this prints:<br><br>One: Uno<br>One: Dos<br><br>Ultimately, I understand why this happens (NetworkRequest’s generic type is always going to be JSONDecodable, no matter if it’s actually a subtype). Is there any way, aside from completely duplicating the class, to call the overload appropriate for the type passed in a class like this? <br><br><br><br>Jon Shier<br>_______________________________________________<br>swift-users mailing list<br>swift-users@swift.org<br>https://lists.swift.org/mailman/listinfo/swift-users<br></div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>