


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


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($;$));

       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
       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 ";




perl v5.10.1                2008-09-29                          1





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


       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).















































perl v5.10.1                2008-09-29                          2


