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[perl5.git] / lib / strict.pm
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1package strict;
2
08d31bcd 3$strict::VERSION = "1.03";
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4
5my %bitmask = (
6refs => 0x00000002,
7subs => 0x00000200,
8vars => 0x00000400
9);
10
11sub 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) {
4b2eca7a 19 require Carp;
e279cb0b 20 Carp::croak("Unknown 'strict' tag(s) '@wrong'");
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21 }
22 $bits;
23}
24
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JH
25my $default_bits = bits(qw(refs subs vars));
26
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27sub import {
28 shift;
08d31bcd 29 $^H |= @_ ? bits(@_) : $default_bits;
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30}
31
32sub unimport {
33 shift;
08d31bcd 34 $^H &= ~ (@_ ? bits(@_) : $default_bits);
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35}
36
371;
38__END__
39
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40=head1 NAME
41
42strict - 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
57If 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
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59casual programming.) Currently, there are three possible things to be
60strict about: "subs", "vars", and "refs".
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61
62=over 6
63
64=item C<strict refs>
65
66This generates a runtime error if you
67use 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
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74 $file = "STDOUT";
75 print $file "Hi!"; # error; note: no comma after $file
f06db76b 76
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77There is one exception to this rule:
78
79 $bar = \&{'foo'};
80 &$bar;
81
82is allowed so that C<goto &$AUTOLOAD> would not break under stricture.
83
84
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85=item C<strict vars>
86
87This generates a compile-time error if you access a variable that wasn't
d66e832e 88declared via C<our> or C<use vars>,
17f410f9 89localized via C<my()>, or wasn't fully qualified. Because this is to avoid
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90variable suicide problems and subtle dynamic scoping issues, a merely
91local() variable isn't good enough. See L<perlfunc/my> and
92L<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
535b5725 99 package Cinna;
17f410f9 100 our $bar; # Declares $bar in current package
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101 $bar = 'HgS'; # ok, global declared via pragma
102
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103The local() generated a compile-time error because you just touched a global
104name without fully qualifying it.
105
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106Because of their special use by sort(), the variables $a and $b are
107exempted from this check.
108
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109=item C<strict subs>
110
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111This disables the poetry optimization, generating a compile-time error if
112you try to use a bareword identifier that's not a subroutine, unless it
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113is a simple identifier (no colons) and that it appears in curly braces or
114on the left hand side of the C<< => >> symbol.
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115
116 use strict 'subs';
117 $SIG{PIPE} = Plumber; # blows up
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118 $SIG{PIPE} = "Plumber"; # just fine: bareword in curlies always ok
119 $SIG{PIPE} = \&Plumber; # preferred form
120
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121=back
122
ee580363 123See L<perlmodlib/Pragmatic Modules>.
f06db76b 124
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125=head1 HISTORY
126
127C<strict 'subs'>, with perl 5.6.1, erroneously permitted to use an unquoted
128compound identifier (e.g. C<Foo::Bar>) as a hash key (before C<< => >> or
129inside curlies), but without forcing it always to a literal string.
130
f06db76b 131=cut