autouse(3)

NNAAMMEE
       autouse - postpone load of modules until a function is
       used

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

DDEESSCCRRIIPPTTIIOONN
       If the module Module is already loaded, then the
       declaration

         use autouse 'Module' => qw(func1 func2($;$) Module::func3);

       is equivalent to

         use Module qw(func1 func2);

       if Module defines func2() with prototype ($;$), and
       func1() and func3() have 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, and declares a function Module::func3().
       When these functions are called, they load the package
       Module if needed, and substitute themselves with the
       correct definitions.

WWAARRNNIINNGG
       Using autouse will move important steps of your program's
       execution from compile time to runtime.  This can

       +o    Break the execution of your program if the module you
            autoused 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
            specified 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
            autouseing gives biggest win, for a workaround see
            below).

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

BBUUGGSS
       If Module::func3() is autoused, and the module is loaded
       between the autouse directive and a call to
       Module::func3(), warnings about redefinition would appear
       if warnings are enabled.

       If Module::func3() is autoused, warnings are disabled when
       loading the module via autoused functions.

AAUUTTHHOORR
       Ilya Zakharevich ilya@math.ohio-state.edu

SSEEEE AALLSSOO
       perl(1).