It can be odd, but it can also be useful as it allows you to more easily override it later without having to go find/replace all instances of @year in your class.
Or, if a class inherits from it and needs to change how year is generated it's easier it doesn't have to worry about parent class using @year.
If that makes sense.
It just seems inconsistent to use year and self.year = ... in the code where one's bare and the other's necessarily prefixed, instead of @year consistently. This plus the way that @year is by default "private".
self.year = ...
One of the major goals of object-oriented design is to properly contain any changes like that, so replacing @year with something else is at least contained to the one file or scope.
Subclass concerns are valid, though in Ruby it's generally understood you need to play nice with your parent's properties and avoid really getting in there and wrecking around.
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