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[perl5.git] / lib / strict.pm
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1package strict;
2
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3$strict::VERSION = "1.04";
4
5# Verify that we're called correctly so that strictures will work.
5108dc18 6unless ( __FILE__ =~ /(^|[\/\\])\Q${\__PACKAGE__}\E\.pmc?$/ ) {
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7 # Can't use Carp, since Carp uses us!
8 my (undef, $f, $l) = caller;
5108dc18 9 die("Incorrect use of pragma '${\__PACKAGE__}' at $f line $l.\n");
e3def60f 10}
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11
12my %bitmask = (
13refs => 0x00000002,
14subs => 0x00000200,
15vars => 0x00000400
16);
17
18sub bits {
19 my $bits = 0;
20 my @wrong;
21 foreach my $s (@_) {
22 push @wrong, $s unless exists $bitmask{$s};
23 $bits |= $bitmask{$s} || 0;
24 }
25 if (@wrong) {
4b2eca7a 26 require Carp;
e279cb0b 27 Carp::croak("Unknown 'strict' tag(s) '@wrong'");
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28 }
29 $bits;
30}
31
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32my $default_bits = bits(qw(refs subs vars));
33
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34sub import {
35 shift;
08d31bcd 36 $^H |= @_ ? bits(@_) : $default_bits;
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37}
38
39sub unimport {
40 shift;
08d31bcd 41 $^H &= ~ (@_ ? bits(@_) : $default_bits);
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42}
43
441;
45__END__
46
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47=head1 NAME
48
49strict - Perl pragma to restrict unsafe constructs
50
51=head1 SYNOPSIS
52
53 use strict;
54
55 use strict "vars";
56 use strict "refs";
57 use strict "subs";
58
59 use strict;
60 no strict "vars";
61
62=head1 DESCRIPTION
63
64If no import list is supplied, all possible restrictions are assumed.
65(This is the safest mode to operate in, but is sometimes too strict for
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66casual programming.) Currently, there are three possible things to be
67strict about: "subs", "vars", and "refs".
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68
69=over 6
70
71=item C<strict refs>
72
73This generates a runtime error if you
74use symbolic references (see L<perlref>).
75
76 use strict 'refs';
77 $ref = \$foo;
78 print $$ref; # ok
79 $ref = "foo";
80 print $$ref; # runtime error; normally ok
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81 $file = "STDOUT";
82 print $file "Hi!"; # error; note: no comma after $file
f06db76b 83
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84There is one exception to this rule:
85
86 $bar = \&{'foo'};
87 &$bar;
88
89is allowed so that C<goto &$AUTOLOAD> would not break under stricture.
90
91
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92=item C<strict vars>
93
94This generates a compile-time error if you access a variable that wasn't
d66e832e 95declared via C<our> or C<use vars>,
17f410f9 96localized via C<my()>, or wasn't fully qualified. Because this is to avoid
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97variable suicide problems and subtle dynamic scoping issues, a merely
98local() variable isn't good enough. See L<perlfunc/my> and
99L<perlfunc/local>.
100
101 use strict 'vars';
102 $X::foo = 1; # ok, fully qualified
103 my $foo = 10; # ok, my() var
104 local $foo = 9; # blows up
105
535b5725 106 package Cinna;
17f410f9 107 our $bar; # Declares $bar in current package
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108 $bar = 'HgS'; # ok, global declared via pragma
109
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110The local() generated a compile-time error because you just touched a global
111name without fully qualifying it.
112
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113Because of their special use by sort(), the variables $a and $b are
114exempted from this check.
115
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116=item C<strict subs>
117
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118This disables the poetry optimization, generating a compile-time error if
119you try to use a bareword identifier that's not a subroutine, unless it
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120is a simple identifier (no colons) and that it appears in curly braces or
121on the left hand side of the C<< => >> symbol.
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122
123 use strict 'subs';
124 $SIG{PIPE} = Plumber; # blows up
5438961c 125 $SIG{PIPE} = "Plumber"; # just fine: quoted string is always ok
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126 $SIG{PIPE} = \&Plumber; # preferred form
127
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128=back
129
ee580363 130See L<perlmodlib/Pragmatic Modules>.
f06db76b 131
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132=head1 HISTORY
133
cbbb4974 134C<strict 'subs'>, with Perl 5.6.1, erroneously permitted to use an unquoted
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135compound identifier (e.g. C<Foo::Bar>) as a hash key (before C<< => >> or
136inside curlies), but without forcing it always to a literal string.
137
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138Starting with Perl 5.8.1 strict is strict about its restrictions:
139if unknown restrictions are used, the strict pragma will abort with
140
141 Unknown 'strict' tag(s) '...'
142
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143As of version 1.04 (Perl 5.10), strict verifies that it is used as
144"strict" to avoid the dreaded Strict trap on case insensitive file
145systems.
146
f06db76b 147=cut