lib/perl5/5.8.8/strict.pm

   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