MAN page from RedHat Other perl-5.004-0.1.i386.rpm

autouse

Section: Perl Programmers Reference Guide (3)
Updated: perl 5.004, patch 04
Index

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($;$) Module::func3);

is equivalent to

  use Module qw(func1 func2);

if Module defines func2() with prototype ($;$), and func1() andfunc3() have no prototypes. (At least if Module uses Exporter'simport, otherwise it is a fatal error.)

If the module Module is not loaded yet, then the above declarationdeclares functions func1() and func2() in the current package, anddeclares a function Module::func3(). When these functions are called,they load the package Module if needed, and substitute themselveswith the correct definitions.

WARNING

Using autouse will move important steps of your program's executionfrom compile time to runtime. This can

•: Break the execution of your program if the module you autoused hassome initialization which it expects to be done early.
•: hide bugs in your code since important checks (like correctness ofprototypes) is moved from compile time to runtime. In particular, ifthe prototype you specified on autouse line is wrong, you will notfind it out until the corresponding function is executed. This will bevery unfortunate for functions which are not always called (note thatfor such functions autouseing gives biggest win, for a workaroundsee below).

To alleviate the second problem (partially) it is advised to writeyour 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 specificationare found early. When you ship your application you should commentout the first line, since it makes the second one useless.

BUGS

If Module::func3() is autoused, and the module is loaded between theautouse directive and a call to Module::func3(), warnings aboutredefinition would appear if warnings are enabled.

If Module::func3() is autoused, warnings are disabled when loading themodule via autoused functions.

AUTHOR

Ilya Zakharevich (ilyaAATTmath.ohio-state.edu)

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