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30:00 - Swift does a lot of extra optimizations and analysis with local vars to try to make this little bit of semantics zero-cost when you don't need it. For example, I don't talk about dynamic exclusivity enforcement in this talk, but we potentially have to use it with local vars if they escape, and yet we really don't want to pay for it if they don't. We also recognize when a reference capture can be a value capture because the value isn't modified after the capture point.