/ 
variable-2009110702
River stage zero No dependents
/ variable

NAME

variable - Perl pragma to declare (scalar) variables without a leading $.

SYNOPSIS

use variable  spam  =>  17;
use variable  eggs  =>  spam + 25;
use variable "i";            # Makes "i" undefined.
use variable  arr   =>  [qw /aap noot mies wim zus jet/];

print eggs, "\n";            # Print 42.
      eggs += 27;
print eggs, "\n";            # Print 69.

for (i = 0; defined (arr -> [i]); i ++) {
    print arr -> [i], " ";   # Print aap noot mies wim zus jet.
}

DESCRIPTION

This simple module allows you to create scalar variables that do not need a leading $. This will make people coming from a C or a Python background feel more at home.

NOTES

This module requires perl 5.6.0.

The values given to the variables are evaluated in list context. You may wish to override this by using scalar.

These variables do not directly interpolate into doublequotish strings, although you may do so indirectly. (See the perlref manpage for details about how this works.)

print "The value of eggs is ${\eggs}.\n";

This only works for scalar variables, not arrays or hashes.

Naming of variables follow the same rules as in constant.pm. Names must begin with a letter or underscore. Names beginning with a double underscore are reserved. Some poor choices for names will generate warnings, if warnings are enabled at compile time.

Variable symbols are package scoped (rather than block scoped, as use strict; is. That is, you can refer to a variable from package Other as Other::var.

As with all use directives, defining a variable happens at compile time. This, it's probably not correct to put a variable declaration inside of a conditional statement (like if ($foo) {use variable ...}).

Omitting the value for a symbol gives it the value of undef. This isn't so nice as it may sound, though, because in this case you must either quote the symbol name, or use a big arrow => with nothing to point to. It is probably best to declare these explicitly.

use variable bacon  =>  ();
use variable ham    =>  undef;

The result from evaluating a list constant in a scalar context is not documented, and is not guaranteed to be any particular value in the future. In particular, you should not rely upon it being the number of elements in the list, especially since it is not necessarily that value in the current implementation.

In the rare case in which you need to discover at run time whether a particular variable has been declared via this module, you may use this function to examine the hash %variable::declared. If the given variable name does not include a package name, the current package is used.

sub declared ($) {
    use variable;                   # don't omit this!
    my $name =  shift;
       $name =~ s/^::/main::/;
    my $pkg  =  caller;
    my $full = $name =~ /::/ ? $name : "${pkg}::$name";
    $variable::declared {$full};
}

BUGS

A variable with the name in the list STDIN STDOUT STDERR ARGV ARGVOUT ENV INC SIG is not allowed anywhere but in package main::, for technical reasons.

You can get into trouble if you use variables in a context which automatically quotes barewords (as is true for any subroutine call). For example, you can't say $hash {variable} because variable will be interpreted as a string. Use $hash {variable ()} or $hash {+variable} to prevent the bareword quoting mechanism from kicking in. Similarly, since the => operator quotes a bareword immediately to its left, you have to say variable () => 'value' (or simple use a comma in place of the big arrow) instead of variable => 'value'

DEVELOPMENT

The current sources of this module are found on github, git://github.com/Abigail/variable.git.

AUTHOR

This package was written by Abigail, cpan@abigail.be.

COPYRIGHT AND LICENSE

Copyright (C) 2000, 2009, Abigail

Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:

The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.

THANKS

The author wishes to thank EFNet's #python IRC channel for the inspiration to write this module.

A lot of the code and documentation of constant.pm was cut and pasted in.