<div dir="ltr">On Tue, Dec 27, 2016 at 4:03 PM, Derrick Ho via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br><div class="gmail_extra"><div class="gmail_quote"><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">I suppose "throws" could be enhanced to produce a compiletime enum <br><br>func bar() throws {<br>throw NSError()<br>throw MyEnumError.firstError<br>}<br><br>Under the hood each expression passed to "throw" could make something like<br><br>enum bar_abcdefj_throw {<br>case genericError // all NSError go here<br>case MyEnumErrorFirstError<br>}<br><br>Where abcdefj is unique characters.<br> <br><br>This enum would only be visible through the catch blocks which would act like a switch statement.<br><br>Speaking of switch statements do they currently support "try" expressions?<br><br>switch try foo() {<br>case .MyEnumErrorFirstError:<br>// handle error<br>default: <br>// handle NSError and everything else<br>}<br></blockquote><div><br></div><div>If I'm not mistaken, `switch try foo()` switches over the return value of foo(); you'd switch over the error in a catch block.</div><div> </div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">The benefit of this approach is that it would be additive. And no source breakage.<br><br>At the risk of being off topic if there is interest in this I can start a new thread for this.<div class="HOEnZb"><div class="h5"><br><div class="gmail_quote"><div dir="ltr">On Tue, Dec 27, 2016 at 9:54 AM Haravikk <<a href="mailto:swift-evolution@haravikk.me" target="_blank">swift-evolution@haravikk.me</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg"><blockquote type="cite" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg">On 27 Dec 2016, at 13:43, Tino Heth <<a href="mailto:2th@gmx.de" class="m_2322409923842249406gmail_msg" target="_blank">2th@gmx.de</a>> wrote:</div><div class="m_2322409923842249406gmail_msg"><div style="word-wrap:break-word" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg">Imho this is no problem:</div><div class="m_2322409923842249406gmail_msg">Right now, we basically have "throws Error", and no matter what is actually thrown, we can always catch exhaustive by keeping the statement unspecific.</div></div></div></div></blockquote><div class="m_2322409923842249406gmail_msg"><br class="m_2322409923842249406gmail_msg"></div></div></div><div style="word-wrap:break-word" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg">True, but for me it's more about knowing what a method can throw; currently to know that you need to consult documentation which, while fine, isn't the best way to do that when the compiler could know and it's then up to you whether to let it auto-complete for all throwable types, or just be generic for some or all of them (or pass the buck).</div></div></div><div style="word-wrap:break-word" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg"><br class="m_2322409923842249406gmail_msg"><blockquote type="cite" class="m_2322409923842249406gmail_msg"><div style="word-wrap:break-word" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg"><blockquote type="cite" class="m_2322409923842249406gmail_msg"><span style="font-family:Monaco" class="m_2322409923842249406gmail_msg">myMethod(args:[String:Any]) throws IOError, IllegalArgumentError? { … }</span></blockquote></div>Imho to much confusion with no real benefit:<div class="m_2322409923842249406gmail_msg">Shouldn't it be up to the caller to decide which errors need special treatment? The library can't enforce proper handling at all.</div></div></blockquote><div class="m_2322409923842249406gmail_msg"><br class="m_2322409923842249406gmail_msg"></div></div></div><div style="word-wrap:break-word" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg">Partly, but it's really just intended to distinguish things that are genuine runtime errors, versus things that shouldn't have happened, i.e- an illegal argument type error shouldn't occur if you're using a method correctly, so it's more like something you might check as an assertion. I should have been more clear that the main difference is in how fix-its might recommend the errors are handled; specific types would produce catch blocks, but optionals might be grouped into a catch-all at the end (e.g- they're special interest that you might not be bothered about), but the compiler would still be aware of them should you decide to add them.</div><div class="m_2322409923842249406gmail_msg"><br class="m_2322409923842249406gmail_msg"></div><div class="m_2322409923842249406gmail_msg">If the distinctions not significant enough though then the "optional" error types could just be ignored for now, I think the more important ability is the ellipsis indicating "plus other errors" so we can specify either exhaustive lists of error types, or keep them open-ended, in which case the types listed are those that would be placed as catch blocks, with the ellipsis indicating that a catch-all is still required (or throw on the current method).</div></div></div><div style="word-wrap:break-word" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg"><br class="m_2322409923842249406gmail_msg"><blockquote type="cite" class="m_2322409923842249406gmail_msg"><div style="word-wrap:break-word" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg">One thing to note with explicit errors is that we'd basically introduce sum types…</div></div></blockquote></div></div><div style="word-wrap:break-word" class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg"></div><br class="m_2322409923842249406gmail_msg"><div class="m_2322409923842249406gmail_msg">Not necessarily; you could think of explicit errors as being doing something like:</div><div class="m_2322409923842249406gmail_msg"><br class="m_2322409923842249406gmail_msg"></div><div class="m_2322409923842249406gmail_msg"><span class="m_2322409923842249406m_7179559898482663862Apple-tab-span m_2322409923842249406gmail_msg" style="white-space:pre-wrap"> </span>enum MyErrorType {</div><div class="m_2322409923842249406gmail_msg"><span class="m_2322409923842249406m_7179559898482663862Apple-tab-span m_2322409923842249406gmail_msg" style="white-space:pre-wrap"> </span>case io_error(IOError)</div><div class="m_2322409923842249406gmail_msg"><span class="m_2322409923842249406m_7179559898482663862Apple-tab-span m_2322409923842249406gmail_msg" style="white-space:pre-wrap"> </span>case illegal_argument(<wbr>IllegalArgumentError)</div><div class="m_2322409923842249406gmail_msg"><span class="m_2322409923842249406m_7179559898482663862Apple-tab-span m_2322409923842249406gmail_msg" style="white-space:pre-wrap"> </span>case unknown(Error)</div><div class="m_2322409923842249406gmail_msg"><span class="m_2322409923842249406m_7179559898482663862Apple-tab-span m_2322409923842249406gmail_msg" style="white-space:pre-wrap"> </span>}</div><div class="m_2322409923842249406gmail_msg"><br class="m_2322409923842249406gmail_msg"></div><div class="m_2322409923842249406gmail_msg">i.e- boilerplate we could do right now, but would prefer not to, but still allowing it to be handled as an enum.</div></div></blockquote></div>
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