Perl Cd Bookshelf [Electronic resources] نسخه متنی

31.2. use autouse

use autouse ''Carp'' => qw(carp croak);
carp "this carp was predeclared and autoused";

This pragma provides a mechanism for run-time demand loading of a
particular module only when a function from that module really gets
called. It does this by providing a stub function that replaces
itself with the real call once triggered. This is similar in spirit
to the way the standard AutoLoader and SelfLoader modules
behave. In short, it''s a performance hack to help make your Perl
program start up faster (on average) by avoiding compilation of modules
that might never ever be called during a given execution run.

How autouse behaves depends on whether the module is already loaded.
For example, if the module Module is already loaded, then the
declaration:

use autouse ''Module'' => qw(func1 func2($;$) Module::func3);

use Module qw(func1 func2);

If, on the other hand, Module has not yet been loaded when the
autouse pragma is parsed, the pragma declares functions func1 and
func2 to be in the current package. It also declares a function
Module::func3 (which could be construed as mildly antisocial, were
it not for the fact that the nonexistence of the Module module
has even more antisocial consequences). When these functions are
called, they make sure the Module in question is loaded and then
replace themselves with calls to the real functions just loaded.

Because the autouse pragma moves portions of your program''s
execution from compile time to run time, this can have unpleasant
ramifications. For example, if the module you autouse has some
initialization that is expected to be done early, this may not happen
early enough. Autousing can also hide bugs in your code when
important checks are moved from compile time to run time.

In particular, if the prototype you''ve specified on autouse line
is wrong, you will not find out about it until the corresponding function
is executed (which may be months or years later, for a rarely called function).
To partially alleviate this problem, you could write your
code like this during code development:

use Chase;
use autouse Chase => qw(hue($) cry(&$));
cry "this cry was predeclared and autoused";