Special variables -- $REFERENCE

$R[EFERENCE]

Approved for inclusion in a future ANSI M[UMPS] language standard.

The value of this variable is equal to the name of the global variable that defined the current value of the "naked indicator" (or is empty when the "naked indicator" is currently undefined).

NAKED() ; Get naked indicator
 IF $REFERENCE="" QUIT "<undefined>"
 NEW TMP
 SET TMP=$DATA(^(0))
 SET TMP=$REFERENCE
 QUIT $EXTRACT(TMP,1,$LENGTH(TMP)-2)

KILL ^ABC
SET ^ABC(1,2,3)="Demo"
WRITE "-->""",$REFERENCE,""""
-->"^ABC(1,2,3)"
SET A=$QUERY(^ABC(1))
WRITE "-->""",A,""", and """,$REFERENCE,"""."
-->"^ABC(1,2,3)", and "".

After a reference to the function $QUERY, the naked indicator becomes undefined, which means that $REFERENCE becomes equal to the empty string.

 ...
 DO SAVNAK
 ...
 DO RESTNAK
 ...
 QUIT
SAVNAK SET OLD=$REFERENCE QUIT
RESTNAK SET $REFERENCE=OLD QUIT

could be used to save and restore the naked indicator. Note that SETting $REFERENCE does not imply that the global variable that it points to is actually referenced, only that the naked indicator is (re)set.

SET X=$DATA(^A(3))
SET ^(3)="data ^A 3 (must be retrieved later)"
SET SBE="$REFERENCE should be equal to "
SET V1=$REFERENCE
WRITE !,SBE,"'^A(3)': ",V1
SET X=$DATA(^(3,4))
SET V2=$REFERENCE
WRITE !,SBE,"'^A(3,4)': ",V2
LOCK ^P(27)
SET V3=$REFERENCE
WRITE !,SBE,"'^A(3,4)': ",V3
SET $REFERENCE=V1
WRITE !,"Naked reference should work: ",^(3)
WRITE !
QUIT

...
SET ^X=1 WRITE !,$REFERENCE
SET ^X(1)=2 WRITE !,$REFERENCE
SET $REFERENCE=""
WRITE !,"Naked indicator is undefined."
should produce:
^X
^X(1)
Note that a reference to ^X makes the naked indicator undefined, but does not make $REFERENCE empty.
The final command, SET $REFERENCE="" makes $REFERENCE empty and also makes the naked indicator undefined.

$REFERENCE may occur as an argument of a NEW command.

        ; Define value of $REFERENCE
        IF $DATA(^Test(1234)
        DO Test1
        WRITE !,"The value of $REFERENCE is "
        WRITE $REFERENCE
        WRITE !,"This value should be ^Test(1234)."
        DO Test2
        WRITE !,"The value of $REFERENCE is "
        WRITE $REFERENCE
        WRITE !,"Should be ^Other(""Name"")."
        QUIT
Test1   NEW $REFERENCE
        DO Test2
        QUIT
Test2   ; Re-define $REFERENCE
        IF $DATA(^Other("Name"))
        QUIT

This document is © Ed de Moel, 1995-2005.
It is part of a book by Ed de Moel that is published under the title "M[UMPS] by Example" (ISBN 0-918118-42-5).
Printed copies of the book are no longer available.

This document describes the various special variables that are defined in the M[UMPS] language standard (ANSI X11.1, ISO 11756).

The information in this document is NOT authoritative and subject to be modified at any moment.
Please consult the appropriate (draft) language standard for an authoritative definition.

In this document, information is included that will appear in future standards.
The MDC cannot guarantee that these 'next' standards will indeed appear.