IBM Informix Developer's Handbook - IBM Redbooks

A quick review of the data type hierarchy is useful. Figure 10-1 shows a summary
of these data types.
Figure 10-1 Hierarchy of data types in Informix servers
The extended data types can be either UDR types or complex data types. We are
especially interested in UDTs, which can be described as follows:
► Distinct: Internally, this data type is stored the same as a source data type,
but it is overlaid with different casts and functions defined beyond the basic
source type. The server sees distinct types as different from the source type.
It is necessary to tell the server:
– Source data type information and how the internal structure is defined.
– The functions of how this data type interacts with its internal structure.
– The operations that are valid with this distinct data type.
– Any secondary access methods on how to handle this type.
– Cast functions to move data in and out of the distinct type are automatic.
► Opaque: A fundamental, user-defined data type. It cannot be broken into
smaller pieces, although it can serve as the building block for other data
types. The internal structure of the opaque data type is invisible to the server.
When you define and use an opaque type, the developer must provide all of
the following:
– How the internal structure is defined.
– The functions that enable routines to interact with its internal structure.
– The operations that are valid with this distinct data type.
– Any secondary access methods on how to handle this type.
– Cast functions to move data in and out of the distinct type need to be
provided.
Chapter 10. User-defined routines 335