Nullable Value Types

TODO

Var #EatsChocolate As Boolean

The variable #EatsChocolate can have one of three values: True, False, or #Null. Its initial value is #Null.

To use a nullable type variable

TODO

Initial values

TODO

Var #TotalUnits As Int

You can use null values to show something is not given or is unknown. If you change #TotalUnits to TotalUnits, then you cannot show that the information is not available.

To set values

TODO

#TotalUnits = 5

TODO

#TotalUnits = #Null

To get values

TODO

To compare nullable variables

When you use nullable Boolean variables in a Boolean expression, the result can be True, False, or #NULL. The truth table that follows gives results for And and Or. Because #b1 and #b2 have three possible values, there are nine mixtures.

#b1#b2#b1 And #b2#b1 Or #b2
#Null#NullNULLNULL
#NullTrueNULLTrue
#NullFalseFalseNULL
True#NullNULLTrue
TrueTrueTrueTrue
TrueFalseFalseTrue
False#NullFalseNULL
FalseTrueFalseTrue
FalseFalseFalseFalse

Nullable types and databases

TODO

See also