1: package strict;
2: 
3: $strict::VERSION = "1.03";
4: 
5: my %bitmask = (
6: refs => 0x00000002,
7: subs => 0x00000200,
8: vars => 0x00000400
9: );
10: 
11: sub bits {
12:     my $bits = 0;
13:     my @wrong;
14:     foreach my $s (@_) {
15: 	push @wrong, $s unless exists $bitmask{$s};
16:         $bits |= $bitmask{$s} || 0;
17:     }
18:     if (@wrong) {
19:         require Carp;
20:         Carp::croak("Unknown 'strict' tag(s) '@wrong'");
21:     }
22:     $bits;
23: }
24: 
25: my $default_bits = bits(qw(refs subs vars));
26: 
27: sub import {
28:     shift;
29:     $^H |= @_ ? bits(@_) : $default_bits;
30: }
31: 
32: sub unimport {
33:     shift;
34:     $^H &= ~ (@_ ? bits(@_) : $default_bits);
35: }
36: 
37: 1;
38: __END__
39: 
40: =head1 NAME
41: 
42: strict - Perl pragma to restrict unsafe constructs
43: 
44: =head1 SYNOPSIS
45: 
46:     use strict;
47: 
48:     use strict "vars";
49:     use strict "refs";
50:     use strict "subs";
51: 
52:     use strict;
53:     no strict "vars";
54: 
55: =head1 DESCRIPTION
56: 
57: If no import list is supplied, all possible restrictions are assumed.
58: (This is the safest mode to operate in, but is sometimes too strict for
59: casual programming.)  Currently, there are three possible things to be
60: strict about:  "subs", "vars", and "refs".
61: 
62: =over 6
63: 
64: =item C<strict refs>
65: 
66: This generates a runtime error if you 
67: use symbolic references (see L<perlref>).
68: 
69:     use strict 'refs';
70:     $ref = \$foo;
71:     print $$ref;	# ok
72:     $ref = "foo";
73:     print $$ref;	# runtime error; normally ok
74:     $file = "STDOUT";
75:     print $file "Hi!";	# error; note: no comma after $file
76: 
77: There is one exception to this rule:
78: 
79:     $bar = \&{'foo'};
80:     &$bar;
81: 
82: is allowed so that C<goto &$AUTOLOAD> would not break under stricture.
83: 
84: 
85: =item C<strict vars>
86: 
87: This generates a compile-time error if you access a variable that wasn't
88: declared via C<our> or C<use vars>,
89: localized via C<my()>, or wasn't fully qualified.  Because this is to avoid
90: variable suicide problems and subtle dynamic scoping issues, a merely
91: local() variable isn't good enough.  See L<perlfunc/my> and
92: L<perlfunc/local>.
93: 
94:     use strict 'vars';
95:     $X::foo = 1;	 # ok, fully qualified
96:     my $foo = 10;	 # ok, my() var
97:     local $foo = 9;	 # blows up
98: 
99:     package Cinna;
100:     our $bar;			# Declares $bar in current package
101:     $bar = 'HgS';		# ok, global declared via pragma
102: 
103: The local() generated a compile-time error because you just touched a global
104: name without fully qualifying it.
105: 
106: Because of their special use by sort(), the variables $a and $b are
107: exempted from this check.
108: 
109: =item C<strict subs>
110: 
111: This disables the poetry optimization, generating a compile-time error if
112: you try to use a bareword identifier that's not a subroutine, unless it
113: is a simple identifier (no colons) and that it appears in curly braces or
114: on the left hand side of the C<< => >> symbol.
115: 
116:     use strict 'subs';
117:     $SIG{PIPE} = Plumber;   	# blows up
118:     $SIG{PIPE} = "Plumber"; 	# just fine: quoted string is always ok
119:     $SIG{PIPE} = \&Plumber; 	# preferred form
120: 
121: =back
122: 
123: See L<perlmodlib/Pragmatic Modules>.
124: 
125: =head1 HISTORY
126: 
127: C<strict 'subs'>, with Perl 5.6.1, erroneously permitted to use an unquoted
128: compound identifier (e.g. C<Foo::Bar>) as a hash key (before C<< => >> or
129: inside curlies), but without forcing it always to a literal string.
130: 
131: Starting with Perl 5.8.1 strict is strict about its restrictions:
132: if unknown restrictions are used, the strict pragma will abort with
133: 
134:     Unknown 'strict' tag(s) '...'
135: 
136: =cut