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  • Scott Paterson thinks this is interesting:

An object must go out of existence neither too late nor too soon. Matters are made more complicated by the fact that multiple objects can have a pointer (a reference) to the very same object. To illustrate, imagine three objects, Manny, Moe, and Jack, where both Manny and Moe have references to Jack:

From

Cover of iOS 11 Programming Fundamentals with Swift

Note

This is an example of how a shared annotation can work.