Opaque-type variables hold data retrieved
from opaque data types. Distinct-type variables hold
data retrieved from distinct data types. If you define a variable
with an opaque data type or a distinct data type, the variable can
only hold data of that type.
If you define an opaque data type
named point and a distinct data type named centerpoint,
you can define SPL variables to hold data from the two types, as the
following figure shows. Figure 1: Defining SPL variables to hold opaque and
distinct data types.
DEFINE a point;
DEFINE b centerpoint;
The variable a can only hold data of type point,
and b can only hold data of type centerpoint.