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<body><div>If it's defined as type Any, then we'd also need a guaranteed compiler optimization (preferably one that happens in debug builds too) that omits the creation of the `Any` value if it's unused.<br></div>
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<div>-Kevin</div>
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<div>On Sat, Dec 5, 2015, at 08:46 PM, Jacob Bandes-Storch wrote:<br></div>
<blockquote type="cite"><div dir="ltr"><div>That approach seems fine to me; I don't think it seems like magic.<br></div>
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<div>"<span class="font" style="font-family:monospace, ' monospace'">if x { returnsAnInt() } else { returnsAString() }</span>" would have type Any, but would only emit a warning if you actually tried to <b>use</b> the value. Much like the current warning, "<i>X inferred to have type Any, which may be unexpected</i>".<br></div>
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<div><div><div dir="ltr"><div>Jacob Bandes-Storch<br></div>
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<div><div>On Sat, Dec 5, 2015 at 7:53 PM, Kevin Ballard via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>></span> wrote:<br></div>
<blockquote style="margin-top:0px;margin-right:0px;margin-bottom:0px;margin-left:0.8ex;border-left-width:1px;border-left-color:rgb(204, 204, 204);border-left-style:solid;padding-left:1ex;"><div><u></u><br></div>
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<div><span>On Sat, Dec 5, 2015, at 04:32 PM, Lukas Stabe via swift-evolution wrote:</span><br></div>
<blockquote type="cite"><div> </div>
<div><blockquote type="cite"><div><span>I don't think you can just get rid of the if statement in favor of an expression. You still want to be able to do this:</span><br></div>
<div><div dir="ltr"><div> </div>
<div><span>if (condition) {</span><br></div>
<div><span> funcWithSideEffectsThatReturnsInt()</span><br></div>
<div><span>} else {</span><br></div>
<div><span> funcWithSideEffectsThatReturnsString()</span><br></div>
<div><span>}</span><br></div>
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<div><span>but that's not a valid expression (what is its type?).</span><br></div>
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<div><span>An if statement with two different types could just have the closes common ancestor or Any as type.</span><br></div>
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<div>That's a great way to cause confusion.<br></div>
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<div>Rust has this feature (all statements are expressions), and it requires if statements to have an else branch with the same type unless the type is `()`. It's solution to the issue of the branches returning unwanted values is that Rust uses semicolons, and the semicolon acts sort of like an operator that consumes any value and returns `()`, so if you terminate the last statement of the branch with a semicolon, the whole branch returns `()`, and if you leave it off, the branch returns a value. It's actually very elegant and straightforward.<br></div>
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<div>That said, proposing that Swift introduce this same rule for semicolons is probably not a good idea. We certainly could declare that an explicit semicolon has this behavior, so you'd see people writing code like<br></div>
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<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">if condition {</span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"> funcWithSideEffectsThatReturnsInt();</span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">}</span><br></div>
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<div>but it would be confusing because semicolons are almost never used in Swift.<br></div>
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<div>An alternative that would work today is just relying on assignment returning Void, so you can write<br></div>
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<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">if condition {</span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"> _ = funcWithSideEffectsThatReturnsInt()</span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">}</span><br></div>
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<div>but that looks kind of weird and would probably also be confusing. Better than the semicolon rule I think, but still not great.<br></div>
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<div>Another option is to check if the return value is actually used anywhere, and if it's not, then silently coerce it to Void. This way you can write<br></div>
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<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">if condition {</span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"> funcWithSideEffectsThatReturnsInt()</span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">} else {</span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"> funcWithSideEffectsThatReturnsString()</span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">}</span><br></div>
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<div>and it would be fine but writing<br></div>
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<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">let foo = if condition {</span><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"> funcWithSideEffectsThatReturnsInt()</span><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">} else {</span><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"> funcWithSideEffectsThatReturnsString()</span><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif"></span><br></div>
<div><span class="font" style="font-family:menlo, consolas, 'courier new', monospace, sans-serif">}</span><br></div>
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<div>would fail with a type error.<br></div>
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<div>I suspect that this is the right approach, but it does involve a bit of magic.<br></div>
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<div>-Kevin<br></div>
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