autouse

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

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 ";

       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 v5.30.0                      2023-11-23                    autouse(3perl)