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The reason for introducing check_owner is to have a believable
function in hand with a class-object, call-by-value parameter. Now that
you have it, note that a railroad_car object is copied
whenever check_owner is called, because the parameter is a
call-by-value parameter:
Memory reserved for Memory reserved for r, railroad_car argument the railroad_car parameter | | v v *-----* Copy *-----* | | -------------> | | |-----| |-----| | | | | |-----| |-----| | | | | |-----| *-----* | | | |-----| | | | | Subclass-specific portion not copied |-----| | | | | *-----*
As you know, only the railroad-car portion of the object is copied, inasmuch as the parameter is declared to be a railroad-car parameter. In this particular situation, only the railroad-car portion is needed, however.