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 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.
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.
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.
Ilya Zakharevich (ilya@math.ohio-state.edu)
perl(1).
If rather than formatting bugs, you encounter substantive content errors in these documents, such as mistakes in the explanations or code, please use the perlbug utility included with the Perl distribution.