When you pass a temp-table and the routine call is local, you can tell the AVM to optimize the call by having the called routine refer to the instance of the temp-table already in the calling routine. You tell the AVM to share a single instance of the temp-table by including the BY-REFERENCE keyword on the caller's RUN statement:

Syntax

RUN internal-procedure-name IN procedure-handle 
  ([ INPUT | INPUT-OUTPUT | OUTPUT ] TABLE temp-table-name BY-REFERENCE 
  )

Passing the caller's temp-table BY-REFERENCE saves all the overhead of copying the temp-table definition and data. If the call is remote, then the AVM ignores the BY-REFERENCE keyword and passes the temp-table by value, as it must in that case.

When you pass a temp-table parameter by reference, the called routine's temp-table definition is bound to the calling routine's temp-table only for the duration of the call.

To pass a temp-table by reference, in the calling routine, use the BY-REFERENCE keyword in the RUN statement that defines the temp-table parameter. There is no special syntax required in the called routine. However, since the calling routine's temp-table instance is substituted for the called routine's temp-table, only the definition of the temp-table is required by the called routine. In other words, the same temp-table is defined in both routines but only one is actually used. If the called routine's temp-table is not directly used to hold its own data anywhere within the routine, you can save the overhead of allocating it by including the REFERENCE-ONLY keyword on its definition:

DEFINE TEMP-TABLE temp-table-name REFERENCE-ONLY.

This keyword tells ABL to use the definition for compiler references to the table and its fields but not to instantiate it at run time. Any reference to the temp-table, except where it is passed in from another routine BY-REFERENCE, results in a runtime error.