0: I had a lot of trouble understanding Perl scoping.  After
1: reading the FAQs, etc, I decided to try writing a program
2: trying out everything.  Now I think I understand it.
3: 
4: This code consists of a program and a perl module.  They
5: should be in the same directory.  Run the program.  It
6: will show how I tried to refer to different declared
7: variables and subs.
8: 
9: This program uses undeclared package variables
10: (terminology correct?), 'my' variables, and 'our'
11: variables.  It doesn't use 'local' variables, though I
12: might change it.  And it also demonstrates using AUTOLOAD
13: subs to react to calls to undefined subs.
14: 
15: I really want this to be useful.  So if you see something
16: I screwed up, or terminology which is wrong, etc, please
17: tell me.  Thanks! -tim allen
18: 
19: (I) THE PROGRAM (scoping.pl)
20: #!/usr/bin/perl
21: # (note: this program will generate a warning if the -w
22: # command line parameter is used.  This is on purpose
23: # to show that 'my' causes variables to be lexically scoped
24: # to their package. -tim)
25: # Program: scoping.pl
26: # Purpose: to try out the various ways of referring to variables
27: # and subs in a package, specifically using "our"
28: # Author: tim allen
29: # Restrictions: 1) I don't "use strict" here on purpose so I
30: #  can have variables not defined as 'my' or 'our'.
31: #  2) I don't declare anything 'local' -- maybe later.
32: 
33: # The AUTOLOAD sub is special: it catches undefined
34: # references to subs.  Programming Perl, p. 297
35: sub AUTOLOAD {
36:   our $AUTOLOAD;
37:   warn "$AUTOLOAD NOT DEFINED IN scoping.pl. (AUTOLOAD)\n";
38:   return undef;
39: }
40: 
41: sub here_sub {
42:   my $in_val = shift;
43:   return "received $in_val in here_sub";
44: }
45: 
46: use Our_package;
47: 
48: # DEFINITIONS
49: # define a package variable for *this* package
50: $package_variable = "defined without 'my' or 'our' in main";
51: # ... and a lexically scoped variable as well
52: my $my_variable = "defined with 'my' in main";
53: # END OF DEFINITIONS
54: 
55: print "VARIABLES IN *THIS* PACKAGE\n";
56: print "1) \$package_variable=$package_variable\n";
57: print "2) \$my_variable=$my_variable\n";
58: 
59: print "\nVARIABLE DECLARED IN *OTHER* PACKAGE\n";
60: print "1) \$our_variable = $our_variable\n" if (defined $our_variable);
61: print "2) \$our_variable NOT DEFINED\n"   if not (defined $our_variable);
62: print "3) \$Our_package::our_variable = $Our_package::our_variable\n";
63: print "4) \$Our_package::my_variable NOT DEFINED\n"
64:   if not (defined $Our_package::my_variable);
65: 
66: print "\nPACKAGE VARIABLE IN OUTSIDE PACKAGE\n";
67: print "1) \$package_variable=$package_variable (WRONG)\n";
68: print "2) \$Our_package::package_variable=$Our_package::package_variable\n";
69: 
70: print "\nCALL SUBROUTINES\n";
71: print "1) Our_package::our_sub(4) = ".Our_package::our_sub(4)."\n";
72: print "2) here_sub(4) = ".here_sub(4)."\n";
73: print "3) here_sub($my_variable) = ".here_sub($my_variable)."\n";
74: 
75: if ($_ = our_sub()) {
76:   print "our_sub() = ".$_."\n"; 
77: }
78: 
79: if ($_ = Our_package::our_foo($my_variable)) {
80:   print "Our_package::our_foo($my_variable) = ".$_."\n";
81: }
82: 
83: (II) AND NOW THE PERL MODULE (Our_package.pm)
84: package Our_package;
85: our $our_variable = "defined with 'our' in Our_package";
86: $package_variable = "defined without 'my' or 'our' in Our_package";
87: my $my_variable = "defined with 'my' in Our_package";
88: 
89: sub AUTOLOAD {
90:   our $AUTOLOAD;
91:   warn "$AUTOLOAD NOT DEFINED IN Our_package.pm.(Our_package::AUTOLOAD)\n";
92:   return undef;
93: }
94: 
95: sub our_sub {
96:   my $in_val = $_[0];
97:   return "defined in Our_package (received $in_val)";
98: }