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[perl5.git] / lib / strict.pm
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1package strict;
2
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3=head1 NAME
4
5strict - Perl pragma to restrict unsafe constructs
6
7=head1 SYNOPSIS
8
9 use strict;
10
11 use strict "vars";
12 use strict "refs";
13 use strict "subs";
14
15 use strict;
16 no strict "vars";
17
18=head1 DESCRIPTION
19
20If no import list is supplied, all possible restrictions are assumed.
21(This is the safest mode to operate in, but is sometimes too strict for
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22casual programming.) Currently, there are three possible things to be
23strict about: "subs", "vars", and "refs".
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24
25=over 6
26
27=item C<strict refs>
28
29This generates a runtime error if you
30use symbolic references (see L<perlref>).
31
32 use strict 'refs';
33 $ref = \$foo;
34 print $$ref; # ok
35 $ref = "foo";
36 print $$ref; # runtime error; normally ok
37
38=item C<strict vars>
39
40This generates a compile-time error if you access a variable that wasn't
535b5725 41declared via C<use vars>,
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42localized via C<my()> or wasn't fully qualified. Because this is to avoid
43variable suicide problems and subtle dynamic scoping issues, a merely
44local() variable isn't good enough. See L<perlfunc/my> and
45L<perlfunc/local>.
46
47 use strict 'vars';
48 $X::foo = 1; # ok, fully qualified
49 my $foo = 10; # ok, my() var
50 local $foo = 9; # blows up
51
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52 package Cinna;
53 use vars qw/ $bar /; # Declares $bar in current package
54 $bar = 'HgS'; # ok, global declared via pragma
55
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56The local() generated a compile-time error because you just touched a global
57name without fully qualifying it.
58
59=item C<strict subs>
60
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61This disables the poetry optimization, generating a compile-time error if
62you try to use a bareword identifier that's not a subroutine, unless it
1fef88e7 63appears in curly braces or on the left hand side of the "=E<gt>" symbol.
cb1a09d0 64
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65
66 use strict 'subs';
67 $SIG{PIPE} = Plumber; # blows up
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68 $SIG{PIPE} = "Plumber"; # just fine: bareword in curlies always ok
69 $SIG{PIPE} = \&Plumber; # preferred form
70
71
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72
73=back
74
ee580363 75See L<perlmodlib/Pragmatic Modules>.
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76
77
78=cut
79
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80$strict::VERSION = "1.01";
81
82my %bitmask = (
83refs => 0x00000002,
84subs => 0x00000200,
85vars => 0x00000400
86);
87
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88sub bits {
89 my $bits = 0;
20408e3c 90 foreach my $s (@_){ $bits |= $bitmask{$s} || 0; };
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91 $bits;
92}
93
94sub import {
95 shift;
55497cff 96 $^H |= bits(@_ ? @_ : qw(refs subs vars));
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97}
98
99sub unimport {
100 shift;
55497cff 101 $^H &= ~ bits(@_ ? @_ : qw(refs subs vars));
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102}
103
1041;