How do built in generic types like map/slice work in Go?

<p>Go doesn&#39;t have generics except for certain built in types (i.e., maps, slices, channels, and arrays). Is there any information on how these generic types are implemented underneath the covers? I&#39;m not readily finding this info and am very curious about the approach taken.</p> <p>Edit: I am <em>not</em> talking about how to implement custom generics in Go. I know that those don&#39;t exist (though some, including me, have hopes for Go 2.0). I&#39;m asking how the exiting Go language implements generics <em>just</em> for the built in maps, channels, slices and arrays. The compiler is doing something when I call make, and I&#39;d like to know what is going on.</p> <hr/>**评论：**<br/><br/>comrade_donkey: <pre><p>Look at e.g. <a href="https://github.com/golang/go/blob/365594ad59873cd8f7fde5ec158067bf695185ee/src/runtime/slice.go#L39"><code>runtime.makeslice</code></a>. It&#39;s what the compiler replaces <code>make([]T, n, m)</code> with. There&#39;s also <a href="https://github.com/golang/go/blob/cbc4e5d9c4f2444c5d40ae6333b4e1f4c9cfbd41/src/runtime/hashmap.go#L270"><code>runtime.makemap</code></a> and analogous functions for other <del>types</del> kinds.</p></pre>unm95: <pre><p><a href="https://www.youtube.com/watch?v=Tl7mi9QmLns" rel="nofollow">https://www.youtube.com/watch?v=Tl7mi9QmLns</a></p></pre>_youtubot_: <pre><p>Video linked by <a href="/u/unm95" rel="nofollow">/u/unm95</a>:</p> <table><thead> <tr> <th align="center">Title</th> <th align="center">Channel</th> <th align="center">Published</th> <th align="center">Duration</th> <th align="center">Likes</th> <th align="center">Total Views</th> </tr> </thead><tbody> <tr> <td align="center"><a href="https://youtube.com/watch?v=Tl7mi9QmLns" rel="nofollow">GopherCon 2016: Keith Randall - Inside the Map Implementation</a></td> <td align="center">Gopher Academy</td> <td align="center">2016-08-18</td> <td align="center">0:26:50</td> <td align="center">92+ (100%)</td> <td align="center">7,206</td> </tr> </tbody></table> <hr/> <p><a href="https://np.reddit.com/r/youtubot/wiki/index" rel="nofollow">^Info</a> ^| <a href="https://np.reddit.com/message/compose/?to=_youtubot_&amp;subject=delete%20comment&amp;message=dm0iz49%0A%0AReason%3A%20%2A%2Aplease+help+us+improve%2A%2A" rel="nofollow">^/u/unm95 ^can ^delete</a> ^| ^v1.1.3b</p></pre>gac_web: <pre><p><a href="https://blog.golang.org/slices" rel="nofollow">https://blog.golang.org/slices</a></p> <p>And Go source is written in Go which makes it relatively easy to read if you know Go.</p></pre>drvd: <pre><p>This is not done as &#34;generics&#34;, these are just types. E.g. <code>struct{a int}</code> and <code>struct{b string}</code> are not treated as specialisations of a generic struct, but well, just types. Same for <code>[]int</code> vs. <code>[]string</code>.</p> <p>The only halfway &#34;generic&#34; is in make, copy and append which just implement what the language spec says about it. These are pretty simple (no &#34;generics&#34; used here). E.g. make just allocates cap*sizeof(elementType) bytes and &#34;zeros&#34; them</p> <p>You won&#39;t find anything useful there to implement generics.</p></pre>itsmontoya: <pre><p>Have you read the source code? It&#39;s literally using generics under the hood</p></pre>drvd: <pre><p>Yes I did. Not it is not. Making a slice is not much more than</p> <pre><code>p := mallocgc(et.size*uintptr(cap), et, true) return slice{p, len, cap} </code></pre> <p>No generics.</p></pre>bartoszgolek: <pre><p>Actualy, there is no way to implement custom generics in Go. There still is discusion undergoing about it, and hopefully generics will be implemented in Go 2.0.</p></pre>jlund3: <pre><p>Edited my post for clarification :)</p></pre>10F1: <pre><p>TL;DR compiler magic.</p></pre>