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-
tion
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 ";
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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(1).
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