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.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>Hi Brent, I understand that <code>SubC.cc as C</code> does not work, that’s the case in my bikeshedding example I noticed that because the enum case is always known at compile time, there will be an error with informs you to downgrade <code>SubC</code> to one of its super-types case. Plus I forget about the <code>RawRepresentable</code> for enums while making this example completely - my bad.</p>
<p>I might not fully understand how sub-typing on value types should work, that’s way I’m looking forward to the document Matthew will write one day. :)</p>
<p>Sub-typing enums to remove cases sounds also really interesting to me. :) </p>
<p>Thank you for your feedback.</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_1486892836494903040" 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 12. Februar 2017 um 09:57:39, Brent Royal-Gordon (<a href="mailto:brent@architechies.com">brent@architechies.com</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>> On Feb 11, 2017, at 2:25 AM, Adrian Zubarev via swift-evolution <swift-evolution@swift.org> wrote:
<br>>
<br>> // Allowed because `C` is open, and open allows sub-typing, conforming
<br>> // and overriding to the client
<br>> enum SubC : C {
<br>> case cc
<br>> }
<br>
<br>There's a subtle mistake here. For a sum type, subtyping actually means *removing* cases, not *adding* cases. (Or it can mean changing some of the associated types into their subtypes, but that's a different story.)
<br>
<br>To understand why, think about casting between `C` and `SubC`. Specifically, imagine this upcast:
<br>
<br> SubC.cc as C
<br>
<br>What is this supposed to do? There is no `cc` case in `C`, so `SubC.cc` cannot be represented as a `C`. That means `SubC` is not a subtype of `C`. In fact, `SubC` would be a *supertype* of `C`—you would need to say `SubC.cc as? C`, but you could always say `C.c as SubC`.
<br>
<br>(The ultimate expression of this is that `Never`—which can be thought of as the subtype of all types—is an empty enum.)
<br>
<br>That's not to say that this is a feature we should add; rather, it's to say that the concept of inheritance doesn't really make any sense for `enum`s.
<br>
<br>Just something I noticed when I was reading this thread. I'll have more to say on the main topic, hopefully soon.
<br>
<br>--
<br>Brent Royal-Gordon
<br>Architechies
<br>
<br></div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>