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
- •
- 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 ";
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).