FromInto

类型会实现 FromInto 以加快类型转换:

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实现 From 后,系统会自动实现 Into

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Speaker Notes

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  • 这就是为什么通常只需实现 From,因为您的类型也会实现 Into
  • 若要声明某个函数实参输入类型(例如“任何可转换成 String 的类型”),规则便会相反,此时应使用 Into。 您的函数会接受可实现 From 的类型,以及那些仅实现 Into 的类型。