<div dir="ltr"><br><br><div class="gmail_quote"><div dir="ltr">On Mon, Dec 26, 2016 at 8:31 PM Daniel Leping via swift-evolution <<a href="mailto:swift-evolution@swift.org">swift-evolution@swift.org</a>> wrote:<br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_msg">Braeden, a good point as for inheritance. Totally agree here.</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">Though the generic factory problem remains. Maybe it could be solved differently? Any ideas?</div></blockquote><div><br></div><div>As a matter of fact, I've used a different approach in some of my own projects that has ended up working out well.</div><div><br></div><div><br></div><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">The only thing that pops up in mind right now is to have some "compiler magic" that deals with the constraints. Maybe a concrete class can fall into the category (be DefaultConstructable).</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">Anyways, my point is that compile time constraints for a type that can be created with a default constructor are important for certain patterns. I'm not saying the protocol is the right or the only way, but I want to find a solution.</div><div class="gmail_msg"><br class="gmail_msg"><div class="gmail_quote gmail_msg"><div class="gmail_msg">On Tue, 27 Dec 2016 at 5:22 Braeden Profile via swift-evolution <<a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a>> wrote:<br class="gmail_msg"></div><blockquote class="gmail_quote gmail_msg" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex"><div style="word-wrap:break-word" class="gmail_msg">I’m gonna do my best to explain my thoughts on this, as I just spent an hour reading the whole thread…………<div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">I’m -1 on adding the protocol DefaultConstructible to the standard library (especially under that name). It doesn’t explain its semantics effectively. I agree that a protocol should have definite semantics that are hopefully explained by the name. This protocol fails that test—a default instance of value types is completely context-specific, and default class instances are just iffy to me.</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">I’m firmly in the camp that you could create a protocol like this for your own project and apply it to the types you think semantically fit the purpose…</div><div class="gmail_msg"><span class="m_4771876137164557897m_-4371823811555265644Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span>protocol ZeroConstructible { init() }</div><div class="gmail_msg"><span class="m_4771876137164557897m_-4371823811555265644Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span>extension Int: ZeroConstructible { }</div><div class="gmail_msg">…but I wouldn’t do this myself, as there are too many use-cases with too many definitions of “default”. What if I wanted Int to conform to multiple? It only can have one init(). I’d do something like this…</div><div class="gmail_msg"><span class="m_4771876137164557897m_-4371823811555265644Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span>protocol ZeroConstructible { static func constructZero() }</div><div class="gmail_msg"><span class="m_4771876137164557897m_-4371823811555265644Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span>protocol UnsafeConstructible { static func constructUnsafe() }</div><div class="gmail_msg"><span class="m_4771876137164557897m_-4371823811555265644Apple-tab-span gmail_msg" style="white-space:pre-wrap"> </span>protocol FactoryConstructible { static func constructDefault() } // I’ve never needed to use a factory, myself...</div><div class="gmail_msg">…and create those new functions when I conform my types to it. It’s cumbersome, but correct. As of yet, I’ve never needed to do such a thing, and nearly all the use-cases brought up in the thread can be solved with something of the like.</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">Every “default" is context-dependant.</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg">Addressing other parts of the thread:</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><ul class="m_4771876137164557897m_-4371823811555265644MailOutline gmail_msg"><li class="gmail_msg">I read a new name suggested for the protocol: “Identity”. Unfortunately, I associate that with the proposed protocol HasIdentity { func === }, not a mathematical identity.</li><li class="gmail_msg">DefaultConstructible could never be a normal protocol that magically gets applied where init() exists. protocol required inits are just that—`required`. If a superclass conforms to DefaultConstructible, every subclass must, too! This would give most every class tree the infinite chain of `init()` that NSObject suffers from.</li><li class="gmail_msg">AnyObject was used to justify compiler magic that could be applied for DefaultConstructible. I disagree that this is appropriate, as AnyObject most certainly implies semantics. Every AnyObject is a class, with reference semantics, unsafe-weak-strong references, and more. I could not see definite semantics evolve for DefaultConstructible throughout the whole discussion.</li></ul><div class="gmail_msg"><br class="gmail_msg"></div></div><div class="gmail_msg">That’s my two cents. Granted, no one would be hurt by its addition except those who try to understand this protocol, but I want to avoid that chaos.</div><div class="gmail_msg"><br class="gmail_msg"></div><div class="gmail_msg"><br class="gmail_msg"></div></div>_______________________________________________<br class="gmail_msg"><br class="gmail_msg">swift-evolution mailing list<br class="gmail_msg"><br class="gmail_msg"><a href="mailto:swift-evolution@swift.org" class="gmail_msg" target="_blank">swift-evolution@swift.org</a><br class="gmail_msg"><br class="gmail_msg"><a href="https://lists.swift.org/mailman/listinfo/swift-evolution" rel="noreferrer" class="gmail_msg" target="_blank">https://lists.swift.org/mailman/listinfo/swift-evolution</a><br class="gmail_msg"><br class="gmail_msg"></blockquote></div></div>
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