Express Either–Or-Relationships as Enums

If you want to encapsulate the notion of “either A or B” (also called “lifting” in functional parlance), an enum type in Swift is the best fit: You can use associated values to wrap types with enums, too: These things seem to be expressible through a common ancestor type or protocol. But bananas and apples can be modeled in totally different manners (apart from sharing nutritional value, for example).

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