How do you fix a retain cycle? Use a weak reference. A weak reference is a pointer that does not imply ownership. To fix our retain cycle, an asset should not own its holder. Edit Asset.h to make holder a weak reference:

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Build and run the program. Note that all the objects are now being deallocated correctly.

In a parent-child relationship, the general rule for preventing this type of retain cycle is the parent owns the child, but the child should not own the parent.