autouse(3) Perl Programmers Reference Guide autouse(3)NAMEautouse - 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 decla
ration
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.
WARNING
Using "autouse" will move important steps of your pro
gram'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 spec
ified 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 appli
cation you should comment out the first line, since it
makes the second one useless.
AUTHOR
Ilya Zakharevich (ilya@math.ohio-state.edu)
SEE ALSOperl(1).
2001-02-22 perl v5.6.1 autouse(3)
