lib:autouse
See the current Perl documentation for lib:autouse.
Here is our local, out-dated (pre-5.6) version:
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.
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 functionsautouse
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).