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171 lines
4.7 KiB
Perl
171 lines
4.7 KiB
Perl
package Symbol;
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=head1 NAME
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Symbol - manipulate Perl symbols and their names
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=head1 SYNOPSIS
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use Symbol;
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$sym = gensym;
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open($sym, "filename");
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$_ = <$sym>;
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# etc.
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ungensym $sym; # no effect
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# replace *FOO{IO} handle but not $FOO, %FOO, etc.
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*FOO = geniosym;
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print qualify("x"), "\n"; # "main::x"
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print qualify("x", "FOO"), "\n"; # "FOO::x"
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print qualify("BAR::x"), "\n"; # "BAR::x"
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print qualify("BAR::x", "FOO"), "\n"; # "BAR::x"
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print qualify("STDOUT", "FOO"), "\n"; # "main::STDOUT" (global)
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print qualify(\*x), "\n"; # returns \*x
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print qualify(\*x, "FOO"), "\n"; # returns \*x
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use strict refs;
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print { qualify_to_ref $fh } "foo!\n";
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$ref = qualify_to_ref $name, $pkg;
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use Symbol qw(delete_package);
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delete_package('Foo::Bar');
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print "deleted\n" unless exists $Foo::{'Bar::'};
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=head1 DESCRIPTION
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C<Symbol::gensym> creates an anonymous glob and returns a reference
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to it. Such a glob reference can be used as a file or directory
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handle.
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For backward compatibility with older implementations that didn't
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support anonymous globs, C<Symbol::ungensym> is also provided.
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But it doesn't do anything.
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C<Symbol::geniosym> creates an anonymous IO handle. This can be
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assigned into an existing glob without affecting the non-IO portions
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of the glob.
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C<Symbol::qualify> turns unqualified symbol names into qualified
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variable names (e.g. "myvar" -E<gt> "MyPackage::myvar"). If it is given a
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second parameter, C<qualify> uses it as the default package;
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otherwise, it uses the package of its caller. Regardless, global
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variable names (e.g. "STDOUT", "ENV", "SIG") are always qualified with
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"main::".
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Qualification applies only to symbol names (strings). References are
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left unchanged under the assumption that they are glob references,
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which are qualified by their nature.
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C<Symbol::qualify_to_ref> is just like C<Symbol::qualify> except that it
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returns a glob ref rather than a symbol name, so you can use the result
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even if C<use strict 'refs'> is in effect.
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C<Symbol::delete_package> wipes out a whole package namespace. Note
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this routine is not exported by default--you may want to import it
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explicitly.
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=head1 BUGS
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C<Symbol::delete_package> is a bit too powerful. It undefines every symbol that
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lives in the specified package. Since perl, for performance reasons, does not
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perform a symbol table lookup each time a function is called or a global
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variable is accessed, some code that has already been loaded and that makes use
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of symbols in package C<Foo> may stop working after you delete C<Foo>, even if
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you reload the C<Foo> module afterwards.
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=cut
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BEGIN { require 5.005; }
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require Exporter;
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@ISA = qw(Exporter);
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@EXPORT = qw(gensym ungensym qualify qualify_to_ref);
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@EXPORT_OK = qw(delete_package geniosym);
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$VERSION = '1.07';
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my $genpkg = "Symbol::";
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my $genseq = 0;
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my %global = map {$_ => 1} qw(ARGV ARGVOUT ENV INC SIG STDERR STDIN STDOUT);
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#
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# Note that we never _copy_ the glob; we just make a ref to it.
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# If we did copy it, then SVf_FAKE would be set on the copy, and
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# glob-specific behaviors (e.g. C<*$ref = \&func>) wouldn't work.
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#
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sub gensym () {
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my $name = "GEN" . $genseq++;
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my $ref = \*{$genpkg . $name};
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delete $$genpkg{$name};
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$ref;
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}
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sub geniosym () {
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my $sym = gensym();
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# force the IO slot to be filled
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select(select $sym);
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*$sym{IO};
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}
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sub ungensym ($) {}
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sub qualify ($;$) {
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my ($name) = @_;
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if (!ref($name) && index($name, '::') == -1 && index($name, "'") == -1) {
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my $pkg;
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# Global names: special character, "^xyz", or other.
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if ($name =~ /^(([^a-z])|(\^[a-z_]+))\z/i || $global{$name}) {
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# RGS 2001-11-05 : translate leading ^X to control-char
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$name =~ s/^\^([a-z_])/'qq(\c'.$1.')'/eei;
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$pkg = "main";
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}
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else {
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$pkg = (@_ > 1) ? $_[1] : caller;
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}
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$name = $pkg . "::" . $name;
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}
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$name;
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}
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sub qualify_to_ref ($;$) {
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return \*{ qualify $_[0], @_ > 1 ? $_[1] : caller };
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}
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#
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# of Safe.pm lineage
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#
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sub delete_package ($) {
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my $pkg = shift;
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# expand to full symbol table name if needed
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unless ($pkg =~ /^main::.*::$/) {
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$pkg = "main$pkg" if $pkg =~ /^::/;
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$pkg = "main::$pkg" unless $pkg =~ /^main::/;
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$pkg .= '::' unless $pkg =~ /::$/;
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}
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my($stem, $leaf) = $pkg =~ m/(.*::)(\w+::)$/;
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my $stem_symtab = *{$stem}{HASH};
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return unless defined $stem_symtab and exists $stem_symtab->{$leaf};
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# free all the symbols in the package
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my $leaf_symtab = *{$stem_symtab->{$leaf}}{HASH};
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foreach my $name (keys %$leaf_symtab) {
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undef *{$pkg . $name};
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}
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# delete the symbol table
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%$leaf_symtab = ();
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delete $stem_symtab->{$leaf};
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}
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1;
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