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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($;$));
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
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Break the execution of your program if the module you autoused has
some initialization which it expects to be done early.
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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 autouseing 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.
Ilya Zakharevich (ilya@math.ohio-state.edu)
perl(1).
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