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Btooom! Chapter 74
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package Symbol;
=head1 NAME
Symbol - manipulate Perl symbols and their names
=head1 SYNOPSIS
use Symbol;
$sym = gensym;
open($sym, '<', "filename");
$_ = <$sym>;
# etc.
ungensym $sym; # no effect
# replace *FOO{IO} handle but not $FOO, %FOO, etc.
*FOO = geniosym;
print qualify("x"), "\n"; # "main::x"
print qualify("x", "FOO"), "\n"; # "FOO::x"
print qualify("BAR::x"), "\n"; # "BAR::x"
print qualify("BAR::x", "FOO"), "\n"; # "BAR::x"
print qualify("STDOUT", "FOO"), "\n"; # "main::STDOUT" (global)
print qualify(\*x), "\n"; # returns \*x
print qualify(\*x, "FOO"), "\n"; # returns \*x
use strict refs;
print { qualify_to_ref $fh } "foo!\n";
$ref = qualify_to_ref $name, $pkg;
use Symbol qw(delete_package);
delete_package('Foo::Bar');
print "deleted\n" unless exists $Foo::{'Bar::'};
=head1 DESCRIPTION
C<Symbol::gensym> creates an anonymous glob and returns a reference
to it. Such a glob reference can be used as a file or directory
handle.
For backward compatibility with older implementations that didn't
support anonymous globs, C<Symbol::ungensym> is also provided.
But it doesn't do anything.
C<Symbol::geniosym> creates an anonymous IO handle. This can be
assigned into an existing glob without affecting the non-IO portions
of the glob.
C<Symbol::qualify> turns unqualified symbol names into qualified
variable names (e.g. "myvar" -E<gt> "MyPackage::myvar"). If it is given a
second parameter, C<qualify> uses it as the default package;
otherwise, it uses the package of its caller. Regardless, global
variable names (e.g. "STDOUT", "ENV", "SIG") are always qualified with
"main::".
Qualification applies only to symbol names (strings). References are
left unchanged under the assumption that they are glob references,
which are qualified by their nature.
C<Symbol::qualify_to_ref> is just like C<Symbol::qualify> except that it
returns a glob ref rather than a symbol name, so you can use the result
even if C<use strict 'refs'> is in effect.
C<Symbol::delete_package> wipes out a whole package namespace. Note
this routine is not exported by default--you may want to import it
explicitly.
=head1 BUGS
C<Symbol::delete_package> is a bit too powerful. It undefines every symbol that
lives in the specified package. Since perl, for performance reasons, does not
perform a symbol table lookup each time a function is called or a global
variable is accessed, some code that has already been loaded and that makes use
of symbols in package C<Foo> may stop working after you delete C<Foo>, even if
you reload the C<Foo> module afterwards.
=cut
BEGIN { require 5.005; }
require Exporter;
@ISA = qw(Exporter);
@EXPORT = qw(gensym ungensym qualify qualify_to_ref);
@EXPORT_OK = qw(delete_package geniosym);
$VERSION = '1.08';
my $genpkg = "Symbol::";
my $genseq = 0;
my %global = map {$_ => 1} qw(ARGV ARGVOUT ENV INC SIG STDERR STDIN STDOUT);
#
# Note that we never _copy_ the glob; we just make a ref to it.
# If we did copy it, then SVf_FAKE would be set on the copy, and
# glob-specific behaviors (e.g. C<*$ref = \&func>) wouldn't work.
#
sub gensym () {
my $name = "GEN" . $genseq++;
my $ref = \*{$genpkg . $name};
delete $$genpkg{$name};
$ref;
}
sub geniosym () {
my $sym = gensym();
# force the IO slot to be filled
select(select $sym);
*$sym{IO};
}
sub ungensym ($) {}
sub qualify ($;$) {
my ($name) = @_;
if (!ref($name) && index($name, '::') == -1 && index($name, "'") == -1) {
my $pkg;
# Global names: special character, "^xyz", or other.
if ($name =~ /^(([^a-z])|(\^[a-z_]+))\z/i || $global{$name}) {
# RGS 2001-11-05 : translate leading ^X to control-char
$name =~ s/^\^([a-z_])/'qq(\c'.$1.')'/eei;
$pkg = "main";
}
else {
$pkg = (@_ > 1) ? $_[1] : caller;
}
$name = $pkg . "::" . $name;
}
$name;
}
sub qualify_to_ref ($;$) {
return \*{ qualify $_[0], @_ > 1 ? $_[1] : caller };
}
#
# of Safe.pm lineage
#
sub delete_package ($) {
my $pkg = shift;
# expand to full symbol table name if needed
unless ($pkg =~ /^main::.*::$/) {
$pkg = "main$pkg" if $pkg =~ /^::/;
$pkg = "main::$pkg" unless $pkg =~ /^main::/;
$pkg .= '::' unless $pkg =~ /::$/;
}
my($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
my $stem_symtab = *{$stem}{HASH};
return unless defined $stem_symtab and exists $stem_symtab->{$leaf};
# free all the symbols in the package
my $leaf_symtab = *{$stem_symtab->{$leaf}}{HASH};
foreach my $name (keys %$leaf_symtab) {
undef *{$pkg . $name};
}
# delete the symbol table
%$leaf_symtab = ();
delete $stem_symtab->{$leaf};
}
1;
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