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autouse(3p)      Perl Programmers Reference Guide     autouse(3p)

       autouse - postpone load of modules until a function is

         use autouse 'Carp' => qw(carp croak);
         carp "this carp was predeclared and autoused ";

       If the module "Module" is already loaded, then the decla-

         use autouse 'Module' => qw(func1 func2($;$));

       is equivalent to

         use Module qw(func1 func2);

       if "Module" defines func2() with prototype "($;$)", and
       func1() has no prototypes.  (At least if "Module" uses
       "Exporter"'s "import", otherwise it is a fatal error.)

       If the module "Module" is not loaded yet, then the above
       declaration declares functions func1() and func2() in the
       current package.  When these functions are called, they
       load the package "Module" if needed, and substitute them-
       selves with the correct definitions.

       Using "autouse" will move important steps of your pro-
       gram's execution from compile time to runtime.  This can

       o   Break the execution of your program if the module you
           "autouse"d has some initialization which it expects to
           be done early.

       o   hide bugs in your code since important checks (like
           correctness of prototypes) is moved from compile time
           to runtime.  In particular, if the prototype you spec-
           ified on "autouse" line is wrong, you will not find it
           out until the corresponding function is executed.
           This will be very unfortunate for functions which are
           not always called (note that for such functions
           "autouse"ing gives biggest win, for a workaround see

       To alleviate the second problem (partially) it is advised
       to write your scripts like this:

         use Module;
         use autouse Module => qw(carp($) croak(&$));
         carp "this carp was predeclared and autoused ";

       The first line ensures that the errors in your argument

perl v5.8.5                 2002-11-06                          1

autouse(3p)      Perl Programmers Reference Guide     autouse(3p)

       specification are found early.  When you ship your appli-
       cation you should comment out the first line, since it
       makes the second one useless.

       Ilya Zakharevich (ilyaATmath.edu)


perl v5.8.5                 2002-11-06                          2