lib/perl5/5.6.1/strict.pm

   1 package strict;
   2
   3 =head1 NAME
   4
   5 strict - 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
  20 If 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
  22 casual programming.)  Currently, there are three possible things to be
  23 strict about:  "subs", "vars", and "refs".
  24
  25 =over 6
  26
  27 =item C<strict refs>
  28
  29 This generates a runtime error if you
  30 use 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     $file = "STDOUT";
  38     print $file "Hi!";  # error; note: no comma after $file
  39
  40 There is one exception to this rule:
  41
  42     $bar = \&{'foo'};
  43     &$bar;
  44
  45 is allowed so that C<goto &$AUTOLOAD> would not break under stricture.
  46
  47
  48 =item C<strict vars>
  49
  50 This generates a compile-time error if you access a variable that wasn't
  51 declared via "our" or C<use vars>,
  52 localized via C<my()>, or wasn't fully qualified.  Because this is to avoid
  53 variable suicide problems and subtle dynamic scoping issues, a merely
  54 local() variable isn't good enough.  See L<perlfunc/my> and
  55 L<perlfunc/local>.
  56
  57     use strict 'vars';
  58     $X::foo = 1;         # ok, fully qualified
  59     my $foo = 10;        # ok, my() var
  60     local $foo = 9;      # blows up
  61
  62     package Cinna;
  63     our $bar;                   # Declares $bar in current package
  64     $bar = 'HgS';               # ok, global declared via pragma
  65
  66 The local() generated a compile-time error because you just touched a global
  67 name without fully qualifying it.
  68
  69 Because of their special use by sort(), the variables $a and $b are
  70 exempted from this check.
  71
  72 =item C<strict subs>
  73
  74 This disables the poetry optimization, generating a compile-time error if
  75 you try to use a bareword identifier that's not a subroutine, unless it
  76 appears in curly braces or on the left hand side of the "=E<gt>" symbol.
  77
  78
  79     use strict 'subs';
  80     $SIG{PIPE} = Plumber;       # blows up
  81     $SIG{PIPE} = "Plumber";     # just fine: bareword in curlies always ok
  82     $SIG{PIPE} = \&Plumber;     # preferred form
  83
  84
  85
  86 =back
  87
  88 See L<perlmodlib/Pragmatic Modules>.
  89
  90
  91 =cut
  92
  93 $strict::VERSION = "1.01";
  94
  95 my %bitmask = (
  96 refs => 0x00000002,
  97 subs => 0x00000200,
  98 vars => 0x00000400
  99 );
 100
 101 sub bits {
 102     my $bits = 0;
 103     foreach my $s (@_){ $bits |= $bitmask{$s} || 0; };
 104     $bits;
 105 }
 106
 107 sub import {
 108     shift;
 109     $^H |= bits(@_ ? @_ : qw(refs subs vars));
 110 }
 111
 112 sub unimport {
 113     shift;
 114     $^H &= ~ bits(@_ ? @_ : qw(refs subs vars));
 115 }
 116
 117 1;