<div dir="ltr">Is there no one that thinks it's sufficient if users can create a tuple from a list of properties and reuse tuple equality and hash?<div><br><div>Is there no one that thinks it's sufficient if the system were to supply a named function for comparing two Any's for equality (with reference equality semantics for reference types, bit equality for value types) that users could use in their type's implementations of ==?</div></div><div><br></div><div>Is there no one that thinks the opt-in mechanism should be a call to a system supplied function, instead of coming up with new keywords or opting in directly through the protocol?</div><div>(Well I know there's at least one person that thinks the opt in mechanism should be by calling a function)</div><div><br></div><div>-- Callionica</div></div><div class="gmail_extra"><br><div class="gmail_quote">On Mon, May 30, 2016 at 12:04 PM, Michael Peternell via swift-evolution <span dir="ltr"><<a href="mailto:swift-evolution@swift.org" target="_blank">swift-evolution@swift.org</a>></span> wrote:<br><blockquote class="gmail_quote" style="margin:0 0 0 .8ex;border-left:1px #ccc solid;padding-left:1ex">It seems that there are two groups here. 1) Group 1 wants Equatable (and others) be derived automatically unless specifically overridden: similar to auto-synthesis of properties in Objective-C. 2) The other group (Group 2) wants Equatable (and others) be derived explicitly using a `deriving` keyword (or something semantically equivalent). Unless I missed something, there were no voices for keeping the status quo, and not introducing any process to automatically derive these protocols.<br>
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I think I chose an easy strategy when proposing the `deriving` keyword. Haskell is a mature language, and "copying" a feature from them is usually a safe choice. For each language feature, someone has to think through all the implications of it; this is usually far from trivial. I argue that if I take a feature from another language, someone has probably already thought about all the pros and cons of different solutions. This is just a plea for embracing precedent.<br>
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There is one advantage of method 2 that (I think) hasn't been discussed so far: when you declare a type `S`, and an `Equatable` instance is automatically derived, there is no way to override that instance in another module. With method 1, there is also no way to request that an `Equatable` instance should *not* be generated. I think no one will vote for something like `struct S @notderiving(Equateble,Hashable) { ... }`.<br>
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Also, a `deriving` keyword is less magical than just automatically deriving `Equatable` and `Hashable` instances. I think the language rules should be as simple as possible, by default. If you want any kind of special behavior, you have to ask for it: `deriving Equatable`, `@IBOutlet`, `@NSManaged`. Furthermore, I think it is good that the developer is aware that there is an "==" method somewhere, specifically for this new type. The compiler should not arbitrarily create methods, because someone may need them. Even if it is very likely that you will need them. Just like in a coffee house, you are asked if you want a coffee, even if you are visiting it every day. For example with Objective-C, I want each developer to be aware of the difference between a property and an iVar, and be aware of the connection between properties, methods, and key-value-coding. The complexities of the language shouldn't be hidden completely.<br>
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Just my two cents..<br>
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-Michael<br>
<div class="HOEnZb"><div class="h5"><br>
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