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
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:
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).