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   1  package Symbol;
   2  
   3  =head1 NAME
   4  
   5  Symbol - manipulate Perl symbols and their names
   6  
   7  =head1 SYNOPSIS
   8  
   9      use Symbol;
  10  
  11      $sym = gensym;
  12      open($sym, "filename");
  13      $_ = <$sym>;
  14      # etc.
  15  
  16      ungensym $sym;      # no effect
  17  
  18      # replace *FOO{IO} handle but not $FOO, %FOO, etc.
  19      *FOO = geniosym;
  20  
  21      print qualify("x"), "\n";              # "Test::x"
  22      print qualify("x", "FOO"), "\n"        # "FOO::x"
  23      print qualify("BAR::x"), "\n";         # "BAR::x"
  24      print qualify("BAR::x", "FOO"), "\n";  # "BAR::x"
  25      print qualify("STDOUT", "FOO"), "\n";  # "main::STDOUT" (global)
  26      print qualify(\*x), "\n";              # returns \*x
  27      print qualify(\*x, "FOO"), "\n";       # returns \*x
  28  
  29      use strict refs;
  30      print { qualify_to_ref $fh } "foo!\n";
  31      $ref = qualify_to_ref $name, $pkg;
  32  
  33      use Symbol qw(delete_package);
  34      delete_package('Foo::Bar');
  35      print "deleted\n" unless exists $Foo::{'Bar::'};
  36  
  37  =head1 DESCRIPTION
  38  
  39  C<Symbol::gensym> creates an anonymous glob and returns a reference
  40  to it.  Such a glob reference can be used as a file or directory
  41  handle.
  42  
  43  For backward compatibility with older implementations that didn't
  44  support anonymous globs, C<Symbol::ungensym> is also provided.
  45  But it doesn't do anything.
  46  
  47  C<Symbol::geniosym> creates an anonymous IO handle.  This can be
  48  assigned into an existing glob without affecting the non-IO portions
  49  of the glob.
  50  
  51  C<Symbol::qualify> turns unqualified symbol names into qualified
  52  variable names (e.g. "myvar" -E<gt> "MyPackage::myvar").  If it is given a
  53  second parameter, C<qualify> uses it as the default package;
  54  otherwise, it uses the package of its caller.  Regardless, global
  55  variable names (e.g. "STDOUT", "ENV", "SIG") are always qualified with
  56  "main::".
  57  
  58  Qualification applies only to symbol names (strings).  References are
  59  left unchanged under the assumption that they are glob references,
  60  which are qualified by their nature.
  61  
  62  C<Symbol::qualify_to_ref> is just like C<Symbol::qualify> except that it
  63  returns a glob ref rather than a symbol name, so you can use the result
  64  even if C<use strict 'refs'> is in effect.
  65  
  66  C<Symbol::delete_package> wipes out a whole package namespace.  Note
  67  this routine is not exported by default--you may want to import it
  68  explicitly.
  69  
  70  =head1 BUGS
  71  
  72  C<Symbol::delete_package> is a bit too powerful. It undefines every symbol that
  73  lives in the specified package. Since perl, for performance reasons, does not
  74  perform a symbol table lookup each time a function is called or a global
  75  variable is accessed, some code that has already been loaded and that makes use
  76  of symbols in package C<Foo> may stop working after you delete C<Foo>, even if
  77  you reload the C<Foo> module afterwards.
  78  
  79  =cut
  80  
  81  BEGIN { require 5.005; }
  82  
  83  require Exporter;
  84  @ISA = qw(Exporter);
  85  @EXPORT = qw(gensym ungensym qualify qualify_to_ref);
  86  @EXPORT_OK = qw(delete_package geniosym);
  87  
  88  $VERSION = '1.06';
  89  
  90  my $genpkg = "Symbol::";
  91  my $genseq = 0;
  92  
  93  my %global = map {$_ => 1} qw(ARGV ARGVOUT ENV INC SIG STDERR STDIN STDOUT);
  94  
  95  #
  96  # Note that we never _copy_ the glob; we just make a ref to it.
  97  # If we did copy it, then SVf_FAKE would be set on the copy, and
  98  # glob-specific behaviors (e.g. C<*$ref = \&func>) wouldn't work.
  99  #
 100  sub gensym () {
 101      my $name = "GEN" . $genseq++;
 102      my $ref = \*{$genpkg . $name};
 103      delete $$genpkg{$name};
 104      $ref;
 105  }
 106  
 107  sub geniosym () {
 108      my $sym = gensym();
 109      # force the IO slot to be filled
 110      select(select $sym);
 111      *$sym{IO};
 112  }
 113  
 114  sub ungensym ($) {}
 115  
 116  sub qualify ($;$) {
 117      my ($name) = @_;
 118      if (!ref($name) && index($name, '::') == -1 && index($name, "'") == -1) {
 119      my $pkg;
 120      # Global names: special character, "^xyz", or other. 
 121      if ($name =~ /^(([^a-z])|(\^[a-z_]+))\z/i || $global{$name}) {
 122          # RGS 2001-11-05 : translate leading ^X to control-char
 123          $name =~ s/^\^([a-z_])/'qq(\c'.$1.')'/eei;
 124          $pkg = "main";
 125      }
 126      else {
 127          $pkg = (@_ > 1) ? $_[1] : caller;
 128      }
 129      $name = $pkg . "::" . $name;
 130      }
 131      $name;
 132  }
 133  
 134  sub qualify_to_ref ($;$) {
 135      return \*{ qualify $_[0], @_ > 1 ? $_[1] : caller };
 136  }
 137  
 138  #
 139  # of Safe.pm lineage
 140  #
 141  sub delete_package ($) {
 142      my $pkg = shift;
 143  
 144      # expand to full symbol table name if needed
 145  
 146      unless ($pkg =~ /^main::.*::$/) {
 147          $pkg = "main$pkg"    if    $pkg =~ /^::/;
 148          $pkg = "main::$pkg"    unless    $pkg =~ /^main::/;
 149          $pkg .= '::'        unless    $pkg =~ /::$/;
 150      }
 151  
 152      my($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
 153      my $stem_symtab = *{$stem}{HASH};
 154      return unless defined $stem_symtab and exists $stem_symtab->{$leaf};
 155  
 156  
 157      # free all the symbols in the package
 158  
 159      my $leaf_symtab = *{$stem_symtab->{$leaf}}{HASH};
 160      foreach my $name (keys %$leaf_symtab) {
 161          undef *{$pkg . $name};
 162      }
 163  
 164      # delete the symbol table
 165  
 166      %$leaf_symtab = ();
 167      delete $stem_symtab->{$leaf};
 168  }
 169  
 170  1;