Condition Compilation Question

I am reading the section regarding conditional compilation here.

http://www.oracle.com/technology/pub/articles/10gdba/nanda_10gr2dba_part1.html#compile

What is the difference for the example below and using a standard "if then else"? Why would below be better? Isn't it evaluated every time?

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Let's examine another variation of this new feature. In addition to the definition of a conditional variable, you can also check a static constant of a package in the conditional compilation. For example, suppose you want to control the debugging output of a PL/SQL procedure based on a Boolean packaged constant. First you create the package as

create or replace package debug_pkg
is
   debug_flag constant boolean := FALSE;
end;

The debug_flag is the constant that determines the conditional logic in the code. You can now embed the code inside the package as follows:

create or replace procedure myproc
as
begin
        $if debug_pkg.debug_flag $then 
                dbms_output.put_line ('Debug=T');
        $else
                dbms_output.put_line ('Debug=F');

        $end
end;

Note that the packaged constant is referenced directly without any $ sign. In this case, there is no need to set any session- or system-level conditional compilation parameters. While the function is compiled, you do not need to pass any additional clause either. To see how this works, execute:

SQL> exec myproc

Debug=F

Because the value of debug_pkg.debug_flag is FALSE now, the execution of the procedure returned "F" as expected. Now, change the constant value:

create or replace package debug_pkg

is
   debug_flag constant boolean := TRUE;
end;

Then, execute the procedure again:

SQL> exec myproc

Debug=T

The procedure picked up the value of the constant to show "T," as expected. Note a very important difference here—you did not need to recompile the procedure; the change to the constant was picked up automatically!

Condition Compilation Question

Ethan Post

2007-05-15