<html><head><meta http-equiv="content-type" content="text/html; charset=utf-8"></head><body dir="auto"><div></div><div>My bad, should have phrased my response better :^)</div><div><br></div><div>Under what circumstances would you need to be able to assign elements in an array out of order, while also requiring Array size/performance? (Genuinely curious, not trying to attack).</div><div><br></div><div>IMO, if the differences between Array and Dictionary would cause that much of an issue for your implementation, my guess is you have more important priorities than the need to assign elements out-of-order 😉 I don't think we'd need to add another type to the standard library for this use case.</div><div><br>On Apr 16, 2017, at 11:22 AM, Saagar Jha <<a href="mailto:saagar@saagarjha.com">saagar@saagarjha.com</a>> wrote:<br><br></div><blockquote type="cite"><div><meta http-equiv="Content-Type" content="text/html charset=utf-8">A Dictionary uses a lot more space than an Array, though, and allow for bogus keys like “-1”, etc.<div class=""><br class=""><div class="">
<div style="color: rgb(0, 0, 0); letter-spacing: normal; orphans: auto; text-align: start; text-indent: 0px; text-transform: none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-stroke-width: 0px; word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space;" class="">Saagar Jha</div>
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<br class=""><div><blockquote type="cite" class=""><div class="">On Apr 16, 2017, at 10:34, Riley Testut via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:</div><br class="Apple-interchange-newline"><div class=""><meta http-equiv="content-type" content="text/html; charset=utf-8" class=""><div dir="auto" class=""><div class=""></div><div class=""><blockquote type="cite" class=""><font class=""><span style="background-color: rgba(255, 255, 255, 0);" class="">Personally, the only valid use-case I can think of is when you want to initialise an Array’s elements out-of-order - i.e., you want to set a value for myArray[2] despite myArray[0] and [1] not being populated. In that case, it would be better to have some kind of SparseArray type, and for us to have a proper API for unsafe initialisation of stdlib types. </span></font></blockquote><br class=""></div><div class="">Wouldn't the same functionality be accomplished by a Dictionary with Int as the key type?</div><div class=""><br class="">On Apr 14, 2017, at 10:00 AM, Karl Wagner via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a>> wrote:<br class=""><br class=""></div><blockquote type="cite" class=""><div class=""><blockquote type="cite" class=""><span class="">I'd actually say the #1 reason not to add this feature is that a lot of developers don't seem to understand this, and they're likely to use the feature to make their code try to continue in the face of programmer error instead of trapping like it properly should. A program in an inconsistent state is dangerous; best to stop it quickly before it does some damage.)</span><br class=""></blockquote><span class=""></span><br class=""><span class="">Right, so I think the reason is actually that a lot of developers don’t understand what an Array is. There are two use-cases for an Array:</span><br class=""><span class=""></span><br class=""><span class="">1) As a string of items, don’t care about the length. The maximum prior knowledge you can have is that the order may or may not be significant. This includes operations like iteration, mapping, reducing and filtering.</span><br class=""><span class="">2) As a string of items of specific length. You have prior knowledge about what you expect to find at each location. This includes operations like random-access subscripting, which is what we’re talking about.</span><br class=""><span class=""></span><br class=""><span class="">Basically, the interesting part of a statement such as “let someValue = myArray[2]” is: why index 2? What’s so special about that element; why couldn't someValue be the item at any index N instead? It’s because we know to expect something of special significance at index 2.</span><br class=""><span class=""></span><br class=""><span class="">In that case, the only time myArray[2] will fail is when your prior knowledge breaks down. The type-system has no way to encode and check for the length of an Array, and that has allowed somebody to pass in a bad value. So what to do?</span><br class=""><span class=""></span><br class=""><span class="">A) If you absolutely require a value for myArray[2]: Insert a precondition check.</span><br class=""><span class="">B) If you can still continue without myArray[2]: Check the length of the Array. Your logic will be branching anyway in this case, to account for the value (and subsequent values) being/not being present.</span><br class=""><span class=""></span><br class=""><span class=""></span><br class=""><span class="">Personally, the only valid use-case I can think of is when you want to initialise an Array’s elements out-of-order - i.e., you want to set a value for myArray[2] despite myArray[0] and [1] not being populated. In that case, it would be better to have some kind of SparseArray type, and for us to have a proper API for unsafe initialisation of stdlib types. </span><br class=""><span class=""></span><br class=""><span class="">- Karl</span><br class=""><span class="">_______________________________________________</span><br class=""><span class="">swift-evolution mailing list</span><br class=""><span class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a></span><br class=""><span class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" class="">https://lists.swift.org/mailman/listinfo/swift-evolution</a></span><br class=""></div></blockquote></div>_______________________________________________<br class="">swift-evolution mailing list<br class=""><a href="mailto:swift-evolution@swift.org" class="">swift-evolution@swift.org</a><br class=""><a href="https://lists.swift.org/mailman/listinfo/swift-evolution">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class=""></div></blockquote></div><br class=""></div></div></blockquote></body></html>