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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

     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 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 `autouse'ing 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.



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



SEE ALSO
     perl(1).









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