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<body><div>We've had multiple threads in the past suggesting many different variants on<br></div>
<div> </div>
<div>if let foo {<br></div>
<div> // foo is non-optional in here<br></div>
<div>}<br></div>
<div> </div>
<div>The only difference with this one is it uses the keyword "bind" instead of any of the various similar alternatives in the other threads.<br></div>
<div> </div>
<div>And my answer is the same to all of this: This is a bad idea. Your construct here does not actually include any notion of assignment or initialization. The construct `if bind foo { ... }` looks like nonsense to anyone who doesn't already explicitly know that it's shorthand for `if let foo = foo { ... }`.<br></div>
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<div>If your goal here is to just avoid having to write the `= foo`, then I disagree with the whole motive. If your goal here is to just use a keyword `bind` instead of `let` (e.g. if you want to use `if bind foo = foo { ... }`), I still disagree, because this new keyword serves no purpose. `if let foo = bar { ... }` is not "fundamentally different" than `let foo = bar`, it's still binding a new identifier to a value, the only difference is it binds it to an optional value. And it's really just a specialization of `if case let foo? = bar { ... }`. I've asked in the past about whether it's worth keeping the special case around now that we have `if case let` (or more specifically, if we should just turn `if let` into the generalized version, so you'd say `if let foo? = bar {... }`) and the answer from the core team was that they already tried it internally and found that the usage of optionals was so prevalent that the special-case optional-specific form of `if let` was worth keeping.<br></div>
<div> </div>
<div>-Kevin Ballard</div>
<div> </div>
<div>On Mon, Feb 1, 2016, at 11:18 AM, Erica Sadun via swift-evolution wrote:<br></div>
<blockquote type="cite"><div>Joe says "<span class="font" style="font-family:Palatino-Roman">If you all are serious about this, I think you should start a new thread about it." </span><br></div>
<div>I think it's worth a serious discussion just so it can be evaluated and either adopted or discarded<br></div>
<div>and dropped forever. Here goes.<br></div>
<div> </div>
<div>INTRO<br></div>
<div><div> </div>
<div>The <span class="font" style="font-family:Menlo">if let x = x {...}</span> and <span class="font" style="font-family:Menlo">guard let x = x else {...}</span> constructs do something with <span class="font" style="font-family:Menlo">let</span> (and <span class="font" style="font-family:Menlo">var</span>) that's <br></div>
<div>fundamentally different from <span class="font" style="font-family:Menlo">let</span> (and <span class="font" style="font-family:Menlo">var</span>) elsewhere in the language. The same keywords are used to conditionally unwrap<br></div>
<div>and bind an item, not just shadow that item's current value.<br></div>
<div> </div>
<div>Introducing a new <span class="font" style="font-family:Menlo">bind</span> keyword to indicate unwrapping and binding would disambiguate these uses.<br></div>
<div> </div>
<div>DETAIL DESIGN:<br></div>
<div> </div>
<div>Jacob Bandes-Storch offers two common use-cases. I prefer his "if bind foo" to my original "if bind foo = foo":<br></div>
<div> </div>
<div><div><span class="font" style="font-family:Menlo"> if bind foo {</span><br></div>
<div><span class="font" style="font-family:Menlo"> // foo is non-optional in here</span><br></div>
<div><span class="font" style="font-family:Menlo"> }</span><br></div>
<div> </div>
<div><span class="font" style="font-family:Menlo"> somethingAsync { [weak self] in</span><br></div>
<div><span class="font" style="font-family:Menlo"> guard bind self else { return }</span><br></div>
<div><span class="font" style="font-family:Menlo"> // ...</span><br></div>
<div><span class="font" style="font-family:Menlo"> }</span><br></div>
</div>
<div> </div>
</div>
<div>JBS's approach offers my original "bind" keyword to unwrap and shadow bind, but also provides a way to <br></div>
<div>strongly bind a weak reference to self, which (presumably) would allow self semantics in the remaining<br></div>
<div>lifetime of that scope.<br></div>
<div> </div>
<div>ALTERNATIVE PROPOSALS:<br></div>
<div> </div>
<div>Tino Heth proposes a second use-case one with different semantics. This case, it seems to make an<br></div>
<div>alias rather than using binding for shadowing:<br></div>
<div> </div>
<div><span class="font" style="font-family:Menlo">bind x = a.property.with.a.long.path<br>print x // 42<br>print(a.property.with.a.long.path == 42) => true</span></div>
<div> </div>
<div><span class="font" style="font-family:Palatino-Roman">presumably this means:</span><br></div>
<div> </div>
<div><span class="font" style="font-family:Menlo">x += 1</span><br></div>
<div><span class="font" style="font-family:Menlo">print(a.property.with.a.long.path) // 43</span><br></div>
<div> </div>
<div><span class="font" style="font-family:Palatino-Roman">DISCUSSION</span><br></div>
<div> </div>
<div><span class="font" style="font-family:Palatino-Roman">I'm throwing these both out there. I have nothing to really say about Tino's but I do think my and Jacob's </span><br></div>
<div><span class="font" style="font-family:Palatino-Roman">proposal has the advantages of:</span><br></div>
<div> </div>
<div><span class="font" style="font-family:Palatino-Roman">* Simplifying an mildly complex and potentially misleading statement </span><br></div>
<div><span class="font" style="font-family:Palatino-Roman">* Creating a deliberate and controlled rather than accidental shadowing style</span><br></div>
<div> </div>
<div><span class="font" style="font-family:Palatino-Roman">Have at it.</span><br></div>
<div> </div>
<div><span class="font" style="font-family:Palatino-Roman">-- Erica</span><br></div>
<div> </div>
<div> </div>
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</blockquote><div> </div>
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