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.send { color:#77bb77; }
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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>This is clearly not a huge issue to solve, but a pitch is a pitch.</p>
<p>From Swift book we know this:</p>
<blockquote>
<p><strong>Switch Statements Must Be Exhaustive</strong></p>
<p>In Swift, every possible value of the control expression’s type must match the value of at least one pattern of a case. When this simply isn’t feasible (for instance, when the control expression’s type is Int), you can include a default case to satisfy the requirement.</p>
</blockquote>
<p>Even for enum values an optional <code>default</code> would mean that you don’t care about the other cases in your current switch, which basically again would be another useless nop.</p>
<pre><code class="swift">enum A {
case a, b, c
}
var value = A.a
switch value {
case .a:
value = A.b
default:
() // I don't care
}
// Do something else
switch value {
case .b:
value = A.c
default:
() // I don't care
}
</code></pre>
<p>Sure the error message is there to notify you that you might forget to handle some case, but how we handle that specific case is still up to us.</p>
<p>I’d really like to know what could be dangerous here when <code>default</code> would be optional.</p>
<p>I can’t tell if this would have some impact on the ABI or not. I’d say it’s additive because it doesn’t break any existing code but removes an existing restriction. </p>
<hr>
<p>The next thought might be an overkill (or maybe not):</p>
<p>How about making <code>default</code> optional everywhere + introducing a new attribute that allows the optional <code>default</code> on that particular enum, but by default every current existing enum should be handled exhaustively.</p>
<p>Bikeshedding:</p>
<pre><code class="swift">enum A {
case a, b, c
}
var value = A.a
switch value {
case .a:
value = A.b
} // Error: switch must be exhaustive, consider adding a default clause
// VS:
@discardableCase enum B {
case d, e, f
}
let anotherValue = B.d
switch anotherValue {
case .d:
// Do something
case .e:
// Do something else
} // Just fine; We don't care here about `.f`
</code></pre>
<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_1475490682107675136" 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 3. Oktober 2016 um 12:28:58, Rien (<a href="mailto:rien@balancingrock.nl">rien@balancingrock.nl</a>) schrieb:</p> <blockquote type="cite" class="clean_bq"><span><div><div></div><div>On non-enum values, yes I could support this. However I do not see this as a big enough issue.
<br>On enum values? no way….
<br>
<br>Btw this would get rid of:
<br>
<br> let bytesSend = send(…) // returns an Int
<br>
<br> switch bytesSend {
<br> case Int.min ... -1: {…}
<br> case 0: {…}
<br> case 1 ... Int.max: {…}
<br> default: break // <<<<<< Imposible
<br> }
<br>
<br>
<br>
<br>
<br>> On 03 Oct 2016, at 12:14, Adrian Zubarev via swift-evolution <swift-evolution@swift.org> wrote:
<br>>
<br>> I know that there is this note in Commonly Rejected Changes:
<br>>
<br>> Remove support for default: in switch and just use case _:: default is widely used, case _ is too magical, and default is widely precedented in many C family languages.
<br>> I really like to use the switch instead of if case for pattern matching, just because it’s neat block design. I do not want to remove default from switches because it’s a must have and powerful feature.
<br>>
<br>> I’d like to know why switches must be exhaustive.
<br>>
<br>> switch someValue {
<br>>
<br>> case …:
<br>> // Do something
<br>>
<br>> case …:
<br>> // Do something else
<br>>
<br>> default:
<br>> () // useless nop; do nothing when no pattern matched
<br>> }
<br>>
<br>> // VS:
<br>>
<br>> if case … {
<br>>
<br>> } else if case … {
<br>>
<br>> } else if case … {
<br>>
<br>> } // No need for `else`
<br>>
<br>> Can’t we make default optional, or at least on non-enum values?
<br>>
<br>>
<br>>
<br>>
<br>> --
<br>> Adrian Zubarev
<br>> Sent with Airmail
<br>>
<br>> _______________________________________________
<br>> swift-evolution mailing list
<br>> swift-evolution@swift.org
<br>> https://lists.swift.org/mailman/listinfo/swift-evolution
<br>
<br></div></div></span></blockquote></div><div class="bloop_markdown"><p></p></div></body></html>