ANYVAR Parameters

An ANYVAR parameter is similar to a VAR parameter in that its actual parameter is passed by reference and must be a variable access. If the routine changes the value of a formal ANYVAR parameter, it changes the value of the actual parameter.

An ANYVAR parameter differs from a VAR parameter in that its actual parameter can be of any type. HP Pascal treats the actual parameter as if it were of the data type of the formal ANYVAR parameter. This is implicit type coercion.

Example 1

$STANDARD_LEVEL 'HP_MODCAL'$
PROGRAM prog;
 
TYPE
   type1 = ARRAY [1..10] OF integer;
   type2 = ARRAY [1..20] OF integer;
   type3 = ARRAY [1..11] OF real;
 
VAR
   var1 : type1;
   var2 : type2;
   var3 : type3;
 
PROCEDURE p (   VAR parm1 : type1;
             ANYVAR parm2 : type2); EXTERNAL;
BEGIN
   p(var1,  {legal}
     var1); {legal}
   p(var2,  {illegal  must be of type1}
     var2); {legal}
   p(var3,  {illegal  must be of type1}
     var3); {legal}
END.

The formal VAR parameter parm1 must have an actual parameter of type type1. The formal ANYVAR parameter parm2 can have an actual parameter of any type.

The first call to procedure p passes the variable var1 (a 10-element integer array) to parm2 (a 20-element integer array). This is legal because parm2 is an ANYVAR parameter; however, parm2[11] through parm2[20] are undefined. Accessing them causes unpredictable results.

The second call to p passes the variable var2 to parm2. Both are 20-element integer arrays. The procedure p can access all 20 elements of parm2.

The third call to p passes the variable var3 (an 11-element real array) to parm2 (a 20-element integer array). Although this is legal, p must not try to access any of the nonexistent elements parm2[12] through parm2[20]. The procedure p treats the elements of parm2 as if they were integers (although the elements of var3 are real).

The implicit type coercion requires that the actual parameter be aligned on a boundary that is the same or larger than the boundary on which the formal parameter is aligned (for example, if the formal parameter is 2-byte-aligned, the actual parameter can be 2-byte-aligned or 4-byte-aligned, but it cannot be byte-aligned).

Example 2

PROGRAM prog;
VAR
   c : PACKED ARRAY [1..2] OF char;
   j : shortint;
   i : integer;
 
PROCEDURE show_anyvar_alignment
          (ANYVAR anyvar_parm : shortint);
          EXTERNAL;
BEGIN
   show_anyvar_alignment(c);  {illegal  must be 2-byte-aligned}
   show_anyvar_alignment(j);  {legal}
   show_anyvar_alignment(i);  {legal  references high-order 2 bytes}
END.

When HP Pascal passes an actual parameter to a formal ANYVAR parameter, it also passes a hidden parameter. The hidden parameter can be used to determine the size of the actual parameter. See “Hidden Parameters ” for more information.