MirOS Manual: autouse(3p)

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


     autouse - postpone load of modules until a function is used


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


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

       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.


     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
         "autouse"d 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 "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 v5.8.8                2005-02-05                           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 applica-
     tion you should comment out the first line, since it makes
     the second one useless.


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



perl v5.8.8                2005-02-05                           2

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