There are three types of directives:
Use the $IF directive to evaluate expressions and determine which code should be included or avoided.
Use the $$identifier syntax to refer to conditional compilation flags. These inquiry directives can be referenced within an $IF directive or used independently in your code.
Use the $ERROR directive to report compilation errors based on conditions evaluated when the preprocessor prepares your code for compilation.
ALTER SESSION SET PLSQL_CCFLAGS = ‘custom_user_parameter:10′; –IF value > $$custom_user_parameter THEN
Name of the compilation unit in which the reference appears
Line number of the compilation unit where the reference appears