$THROWOBJ contains the object reference (OREF) thrown by the most recent unsuccessful THROW operation. InterSystems IRIS writes an OREF to $THROWOBJ when it issues a <THROW> error. Commonly, this occurs when attempting to issue a THROW when not inside a TRY or CATCH block.
A successful THROW operation resets $THROWOBJ to the empty string.
For information on TRY, THROW, and CATCH, see “The TRY-CATCH Mechanism” in the “Error Processing” chapter of Using ObjectScript.
For information on OREFs, see “OREF Basics” in Defining and Using Classes.
You can also explicitly reset $THROWOBJ as follows:
$THROWOBJ cannot be set to any value other than the empty string using the SET command. Attempting to do so results in a <ILLEGAL VALUE> error.