<html><head><style>body{font-family:Helvetica,Arial;font-size:13px}</style></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;"><div id="bloop_customfont" style="font-family:Helvetica,Arial;font-size:13px; color: rgba(0,0,0,1.0); margin: 0px; line-height: auto;">So the typed throws are going to be limited to a single error type, is that the direction we're heading to?</div> <br> <div id="bloop_sign_1487360439950413824" 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 17. Februar 2017 um 20:39:12, Anton Zhilin (<a href="mailto:antonyzhilin@gmail.com">antonyzhilin@gmail.com</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>
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<p style="margin:0px 0px 1.2em!important">In this case, you’d
better create a new error type, which includes all the cases of
those errors:</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important">// FileNotFoundError and WrongFormat are Error-s
struct PreferencesError : Error {
init(_: FileNotFoundError)
init(_: WrongFormat)
// ...
}
func readPreferences() throws(PreferencesError)
</code></pre>
<p style="margin:0px 0px 1.2em!important">In the most “lazy” case,
you’d just create an enum of those two:</p>
<pre style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;font-size:1em;line-height:1.2em;margin:1.2em 0px"><code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline;white-space:pre;overflow:auto;border-radius:3px;border:1px solid rgb(204,204,204);padding:0.5em 0.7em;display:block!important">enum PreferencesError : Error {
case fileNotFound(FileNotFoundError)
case wrongFormat(WrongFormatError)
}
</code></pre>
<p style="margin:0px 0px 1.2em!important">Better yet, you should
analyze, which cases are meaningful for user of <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline">
readPreferences</code>, and present them with appropriate
interface. You may want to crash on those cases of initial error
types, with which you can’t do anything on the level of abstraction
of <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline">
readPreferences</code>. Some of the others will be merged or
renamed.</p>
<p style="margin:0px 0px 1.2em!important">With proper error types,
a single type in <code style="font-size:0.85em;font-family:Consolas,Inconsolata,Courier,monospace;margin:0px 0.15em;padding:0px 0.3em;white-space:pre-wrap;border:1px solid rgb(234,234,234);background-color:rgb(248,248,248);border-radius:3px;display:inline">
throws</code> clause is enough, without sum types.</p>
<p style="margin:0px 0px 1.2em!important">2017-02-17 22:22
GMT+03:00 Adrian Zubarev via swift-evolution <<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>>:</p>
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<p>Sure thing, but that’s not what I was asking about. Kevin made a
protocol that conforms to <code>Error</code> where all the his
enums conformed to <code>MyError</code> protocol. That way we’re
losing all enum cases and are not really a step further as
before.</p>
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