Oracle 10gR2+ conditional PL/SQL Compilation

Oracle Database 10g Release 2 delivers a new PL/SQL language feature: conditional compilation. The feature is elegant and easy to understand.

There are three kinds of PL/SQL conditional compilation construct: the selection directive, the inquiry directive, and the error directive. Code_1 uses all of these. The
following sections discuss them in detail and suggest some best-practice principles for their use.

The selection directive

The motivating requirement for conditional compilation is that it must select between alternative fragments of source text at compilation time. PL/SQL
conditional compilation satisfies this requirement with the selection directive. Code_2 illustrates this.

Code_2 relies on the package CC_Control: Code_2

$if CC_Control.Trace_Level > 0 $then
  Print(Sparse_Collection.Count());
   $if CC_Control.Trace_Level > 1 $then
    declare Idx Idx_t := Sparse_Collection.First();
    begin
      while Idx is not null loop
        Print(Idx||' '||Sparse_Collection(Idx));
        Idx := Sparse_Collection.Next(Idx);
      end loop;
    end;
  $end
$end

package CC_Control is

Trace_Level constant pls_integer := 2;
end CC_Control;
package CC

The selection directive must test a so-called static boolean expression. The rules that such an expression must satisfy are defined in the PL/SQL User’s Guide and
Reference book; the evaluation of a static expression must always give the same result unless anything it depends on — a static package constant or the result of
an inquiry directive (see The inquiry directive on page 9) — has been deliberately changed. A static boolean expression must be composed using so-called static
package constants, literals, or inquiry directives. Thus, for example, d in the following is not a static package constant:

package CC_Control is
  ...
  d constant pls_integer := To_Char(Sysdate, 'J');
end CC_Control;

Therefore, the following is not a static boolean expression

CC_Control.d > 0 or CC_Control.Trace_Level

The selection directive uses these special building blocks

$if $then $elsif $else $end

The meaning of each is exactly symmetrical with that of the corresponding run-time if building block. (Notice, though, that the selection directive ends with just $end
rather than with $end $if.) The rules for evaluating the static boolean expression that the selection directive uses
are the same rules that PL/SQL uses at run-time. In particular, null has its usual significance.

Examples

create or replace procedure p
as
begin
  $IF $$debug_code
  $THEN
    dbms_output.put_line( 'Our debug code' );
    dbms_output.put_line( 'Would go here' );
  $END
  dbms_output.put_line( 'And our real code here' );
end;
/

alter procedure P compile
plsql_ccflags = 'debug_code:true' reuse settings
/

create or replace procedure p2
as
begin
 $if $$plsql_debug
 $then
    $error 'This program must be compiled with PLSQL_DEBUG disabled' $end
 $end
 dbms_output.put_line( 'This is where it happens!' );
end;
/
Procedure created
ALTER SESSION SET PLSQL_DEBUG=TRUE
/
alter procedure p2 compile
/
Warning: Procedure altered with compilation errors.
show err
Errors for PROCEDURE P2:
LINE/COL ERROR
-------- -----------------------------------------------------------------
6/5      PLS-00179: $ERROR: This program must be compiled with PLSQL_DEBUG
         disabled