autouse(3)                                                          autouse(3)



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

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


DESCRIPTION
     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.

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

     ⊕    Break the execution of your program if the module you autoused has
          some initialization which it expects to be done early.

     ⊕    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.



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autouse(3)                                                          autouse(3)



BUGS
     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.

AUTHOR
     Ilya Zakharevich (ilya@math.ohio-state.edu)

SEE ALSO
     perl(1).










































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