Samson Monaco Tutankhamen > File-Package-0.06 > File::Package

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Module Version: 1.16   Source  

NAME ^

File::Package - test load a pm and import symbols without eval and $@ misbehavoirs

SYNOPSIS ^

 ##########
 # Subroutine interface
 #
 use File::Package qw(is_package_loaded load_package);

 $yes = is_package_loaded($package, $program_module);

 $error   = load_package($program_module);
 $error   = load_package($program_module, @import);
 $error   = load_package($program_module, [@package_list]);
 $error   = load_package($program_module, @import, [@package_list]);

 ##########
 # Class Interface
 # 
 use File::Package;

 $yes = is_package_loaded($package, $program_module);

 $error   = File::Package->load_package($program_module);
 $error   = File::Package->load_package($program_module, @import);
 $error   = File::Package->load_package($program_module, [@package_list]);
 $error   = File::Package->load_package($program_module, @import, [@package_list]);

DESCRIPTION ^

In a perfect Perl, everything would behave exactly the same running under eval. Many times the reason to use an eval is the anticipation that the expression may die. When that happens, a perfect Perl would have deposited all the output fromm the warn and die in $@. Maybe you have a perfect Perl. However, it is shocking that there are some Perls on some platforms out in the wild that are mutants and are not perfect.

A require under eval works just fine just to see if a program will load or not. If working locally, you can simply devise a quick debug setup and track down the problem. However, when running tests remotely, on different remote platforms, running continuously unattended where uptime is important, or any number of situations it is very helpful to have meaningful error messages when a problem arise.

Thus, the reason to run under eval is not only to avoid the die but also to pick up the error message returned by eval in $@. In certain situations it is extremely critical to obtain reliable error messages when a failure occurs.

Well, a eval "require $program_module" failure returns a reasonble looking $@ except for one small thing. Not all the warnings make it to $@ at least on one Perl, probably more. And there can be quite a few warnings when loading a broken program module. It would be nice if everyone could update to a Perl where the eval deposits all the warnings in $@. But as the acient proverb says, "If wishes were horses, beggers would ride.".

One workaround is to catch the warnings with $SIG{__WARN__} when running the require under a eval. This collects all the warnings which is good. Now when a load fails, the program does not die, it gracefully collects all the warnings and logs them or ships back.

Now try the import under eval and pick up the error messages. The import and eval is big time "failure to communicate" aka the movie "Cool Hand Luke". The import uses the caller stack to determine where to stuff the symbols and there is a lot of Carp croak gyrations such as making import look like use, trapping warnings and dies. The eval takes off on its own caller stack which to quote President Bush: "is not helpful".

The import uses the croak instead of die directly or else any efforts to get meaningfull error messages would be dead on arrival. Perl is designed so that it is nearly impossible to avoid a die unless running under a eval. A workaround is hooking in a croak that does not die and collecting the error messages.

Subroutines ^

is_package_loaded

 $package = is_package_loaded($program_module, $package)

The is_package_loaded subroutine determines if the $package is present and the $progarm_module loaded. If $package is absent, 0 or '', $package is set to the program_module.

load_package

  $error = load_package($program_module, @import, [@package_list]);

The load_package subroutine attempts to capture any load problems by loading the package with a "require " under an eval and capturing all the "warn" and $@ messages.

If the $program_module load is successful, the checks that the packages in the @package list are present. If @package list is absent, the $program_module uses the program_module name as a list of one package. Although a program module and package have the same name syntax, they are entirely different. A program module is a file. A package is a hash of symbols, a symbol table. The Perl convention is that the names for each are the same which enhances the appearance that they are the same when in fact they are different. Thus, a program module may have a single package with a different name or many different packages.

Finally the $program_module subroutine will import the symbols in the @import list. If @import is absent $program_module subroutine does not import any symbols; if @import is '', all symbols are imported. A @import of 0 usually results in an $error.

The $program_module traps all load errors and all import Carp::Crock errors and returns them in the $error string.

One very useful application of the load_package subroutine is in test scripts. If a package does load, it is very helpful that the program does not die and reports the reason the package did not load. This information is readily available when loaded at a local site. However, it the load occurs at a remote site and the load crashes Perl, the remote tester usually will not have this information readily available.

Other applications include using backup alternative software if a package does not load. For example if the package 'Compress::Zlib' did not load, an attempt may be made to use the gzip system command.

BUGS ^

The load_package cannot load program modules whose name contain the '-' characters. The 'eval' function used to trap the die errors believes it means subtraction.

REQUIREMENTS ^

Coming.

DEMONSTRATION ^

 #########
 # perl Package.d
 ###

 ~~~~~~ Demonstration overview ~~~~~

Perl code begins with the prompt

 =>

The selected results from executing the Perl Code follow on the next lines. For example,

 => 2 + 2
 4

 ~~~~~~ The demonstration follows ~~~~~

 =>     use File::Package;
 =>     my $uut = 'File::Package';

 => ##################
 => # Good Load
 => # 
 => ###

 => my $error = $uut->load_package( 'File::Basename' )
 ''

 => $error = $uut->load_package( '_File_::BadLoad' )
 'Cannot load _File_::BadLoad
        syntax error at E:/User/SoftwareDiamonds/installation/t/File/_File_/BadLoad.pm line 13, near "$FILE "
        Global symbol "$FILE" requires explicit package name at E:/User/SoftwareDiamonds/installation/t/File/_File_/BadLoad.pm line 13.
        Compilation failed in require at (eval 12) line 1.
        Scalar found where operator expected at E:/User/SoftwareDiamonds/installation/t/File/_File_/BadLoad.pm line 13, near "$FILE"
                (Missing semicolon on previous line?)
        '

 => $uut->load_package( '_File_::BadPackage' )
 '# _File_::BadPackage file but package(s) _File_::BadPackage absent.
 '

 => $uut->load_package( '_File_::Multi' )
 '# _File_::Multi file but package(s) _File_::Multi absent.
 '

 => $error = $uut->load_package( '_File_::Hyphen-Test' )
 'Cannot load _File_::Hyphen-Test
        syntax error at (eval 15) line 1, near "require _File_::Hyphen-"
        Warning: Use of "require" without parens is ambiguous at (eval 15) line 1.
        '

 => ##################
 => # No &File::Find::find import baseline
 => # 
 => ###

 => !defined($main::{'find'})
 '1'

 => ##################
 => # Load File::Find, Import &File::Find::find
 => # 
 => ###

 => $error = $uut->load_package( 'File::Find', 'find', ['File::Find'] )
 ''

 => ##################
 => # &File::Find::find imported
 => # 
 => ###

 => defined($main::{'find'})
 '1'

 => ##################
 => # &File::Find::finddepth not imported
 => # 
 => ###

 => !defined($main::{'finddepth'})
 '1'

 => ##################
 => # Import error
 => # 
 => ###

 => $uut->load_package( 'File::Find', 'Jolly_Green_Giant')
 '"Jolly_Green_Giant" is not exported by the File::Find module
 Can't continue after import errors at D:/Perl/lib/Exporter/Heavy.pm line 127
        Exporter::heavy_export('File::Find', 'main', 'Jolly_Green_Giant') called at D:/Perl/lib/Exporter.pm line 45
        Exporter::import('File::Find', 'Jolly_Green_Giant') called at (eval 9) line 81
        File::Package::load_package('File::Package', 'File::Find', 'Jolly_Green_Giant') called at E:\User\SoftwareDiamonds\installation\t\File\Package.d line 195
 '

 => ##################
 => # &File::Find::finddepth still no imported
 => # 
 => ###

 => !defined($main::{'finddepth'})
 '1'

 => ##################
 => # Import all File::Find functions
 => # 
 => ###

 => $error = $uut->load_package( 'File::Find', '')
 ''

 => ##################
 => # &File::Find::finddepth imported
 => # 
 => ###

 => defined($main::{'finddepth'})
 '1'

QUALITY ASSURANCE ^

Running the test script package.t verifies the requirements for this module.

The <tmake.pl> cover script for Test::STDmaker automatically generated the package.t test script, package.d demo script, and t::File::Package STD program module POD, from the t::File::Package program module contents. The t::File::Package program module is in the distribution file File-Package-$VERSION.tar.gz.

NOTES ^

AUTHOR

The holder of the copyright and maintainer is

<support@SoftwareDiamonds.com>

COPYRIGHT NOTICE

Copyrighted (c) 2002 Software Diamonds

All Rights Reserved

BINDING REQUIREMENTS NOTICE

Binding requirements are indexed with the pharse 'shall[dd]' where dd is an unique number for each header section. This conforms to standard federal government practices, 490A ("3.2.3.6" in STD490A). In accordance with the License, Software Diamonds is not liable for any requirement, binding or otherwise.

LICENSE

Software Diamonds permits the redistribution and use in source and binary forms, with or without modification, provided that the following conditions are met:

  1. Redistributions of source code must retain the above copyright notice, this list of conditions and the following disclaimer.
  2. Redistributions in binary form must reproduce the above copyright notice, this list of conditions and the following disclaimer in the documentation and/or other materials provided with the distribution.

SOFTWARE DIAMONDS, http::www.softwarediamonds.com, PROVIDES THIS SOFTWARE 'AS IS' AND ANY EXPRESS OR IMPLIED WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT SHALL SOFTWARE DIAMONDS BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE,DATA, OR PROFITS; OR BUSINESS INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING USE OF THIS SOFTWARE, EVEN IF ADVISED OF NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY OUT OF THE POSSIBILITY OF SUCH DAMAGE.

SEE ALSO ^

Docs::Site_SVD::File_Package
Test::STDmaker
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