<div dir="ltr"><div class="markdown-here-wrapper" style=""><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 &lt;<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>&gt;:</p>
<p style="margin:0px 0px 1.2em!important"></p><div class="markdown-here-exclude"><p></p><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word"><div class="m_7383326189739117365bloop_markdown"><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></div></div></blockquote><p></p></div><p style="margin:0px 0px 1.2em!important"></p>
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