The Nullable<T> type lets us make any value type nullable. But why is this useful? When might we want to store a null value in a type, in addition to the normal range of values?
It’s often useful to represent the fact that a variable doesn’t have a value.
For example, assume that we have a class that stores some information about a book that we have read. We might have a DateStarted and a DateFinished field:
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| DateTime DateStarted;DateTime DateFinished; |
If we want to be able to store information representing a book that has been started, but not yet finished, we’d want to store a value for DateStarted, but no value for DateFinished. With a normal DateTime value, we couldn’t do this. Instead, we make both fields nullable, allowing us to store a null value for either.
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| DateTime? DateStarted;DateTime? DateFinished; |