But you can make it work for your types! mikeash.com/pyblog/friday-
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Reminder that copy-on-write in Swift is a feature of Array, Dictionary, etc… not of structs in general. It’s not automatic for your types.
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really!? so all this time, when we’ve been saying “value semantics”, they’re not equal for all value types?
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Huh? No, copy-on-write-ness is what’s different. That’s not part of semantics—it’s an optimization.
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I do feel a little misled. Strange to learn this on Twitter rather than in a wwdc talk.
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I think a key thing to realize is that the compiler can elide copies often. Dynamic cases need this.
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yeah I previously figured compiler would make decision on cow vs eager copying for all value types