autouse(3pm) Perl Programmers Reference Guide autouse(3pm)
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 v5.38.2 2023-11-28 autouse(3pm)
perl 5.38.2 - Generated Sun Dec 15 13:09:46 CST 2024