468 lines
14 KiB
Perl
468 lines
14 KiB
Perl
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package Exporter;
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require 5.001;
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#
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# We go to a lot of trouble not to 'require Carp' at file scope,
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# because Carp requires Exporter, and something has to give.
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#
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$ExportLevel = 0;
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$Verbose = 0 unless $Verbose;
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sub export {
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# First make import warnings look like they're coming from the "use".
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local $SIG{__WARN__} = sub {
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my $text = shift;
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if ($text =~ s/ at \S*Exporter.pm line \d+.*\n//) {
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require Carp;
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local $Carp::CarpLevel = 1; # ignore package calling us too.
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Carp::carp($text);
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}
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else {
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warn $text;
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}
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};
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local $SIG{__DIE__} = sub {
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require Carp;
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local $Carp::CarpLevel = 1; # ignore package calling us too.
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Carp::croak("$_[0]Illegal null symbol in \@${1}::EXPORT")
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if $_[0] =~ /^Unable to create sub named "(.*?)::"/;
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};
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my($pkg, $callpkg, @imports) = @_;
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my($type, $sym, $oops);
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*exports = *{"${pkg}::EXPORT"};
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if (@imports) {
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if (!%exports) {
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grep(s/^&//, @exports);
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@exports{@exports} = (1) x @exports;
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my $ok = \@{"${pkg}::EXPORT_OK"};
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if (@$ok) {
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grep(s/^&//, @$ok);
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@exports{@$ok} = (1) x @$ok;
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}
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}
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if ($imports[0] =~ m#^[/!:]#){
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my $tagsref = \%{"${pkg}::EXPORT_TAGS"};
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my $tagdata;
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my %imports;
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my($remove, $spec, @names, @allexports);
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# negated first item implies starting with default set:
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unshift @imports, ':DEFAULT' if $imports[0] =~ m/^!/;
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foreach $spec (@imports){
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$remove = $spec =~ s/^!//;
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if ($spec =~ s/^://){
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if ($spec eq 'DEFAULT'){
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@names = @exports;
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}
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elsif ($tagdata = $tagsref->{$spec}) {
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@names = @$tagdata;
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}
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else {
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warn qq["$spec" is not defined in %${pkg}::EXPORT_TAGS];
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++$oops;
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next;
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}
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}
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elsif ($spec =~ m:^/(.*)/$:){
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my $patn = $1;
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@allexports = keys %exports unless @allexports; # only do keys once
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@names = grep(/$patn/, @allexports); # not anchored by default
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}
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else {
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@names = ($spec); # is a normal symbol name
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}
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warn "Import ".($remove ? "del":"add").": @names "
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if $Verbose;
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if ($remove) {
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foreach $sym (@names) { delete $imports{$sym} }
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}
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else {
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@imports{@names} = (1) x @names;
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}
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}
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@imports = keys %imports;
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}
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foreach $sym (@imports) {
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if (!$exports{$sym}) {
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if ($sym =~ m/^\d/) {
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$pkg->require_version($sym);
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# If the version number was the only thing specified
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# then we should act as if nothing was specified:
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if (@imports == 1) {
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@imports = @exports;
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last;
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}
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# We need a way to emulate 'use Foo ()' but still
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# allow an easy version check: "use Foo 1.23, ''";
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if (@imports == 2 and !$imports[1]) {
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@imports = ();
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last;
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}
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} elsif ($sym !~ s/^&// || !$exports{$sym}) {
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require Carp;
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Carp::carp(qq["$sym" is not exported by the $pkg module]);
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$oops++;
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}
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}
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}
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if ($oops) {
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require Carp;
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Carp::croak("Can't continue after import errors");
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}
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}
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else {
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@imports = @exports;
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}
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*fail = *{"${pkg}::EXPORT_FAIL"};
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if (@fail) {
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if (!%fail) {
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# Build cache of symbols. Optimise the lookup by adding
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# barewords twice... both with and without a leading &.
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# (Technique could be applied to %exports cache at cost of memory)
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my @expanded = map { /^\w/ ? ($_, '&'.$_) : $_ } @fail;
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warn "${pkg}::EXPORT_FAIL cached: @expanded" if $Verbose;
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@fail{@expanded} = (1) x @expanded;
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}
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my @failed;
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foreach $sym (@imports) { push(@failed, $sym) if $fail{$sym} }
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if (@failed) {
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@failed = $pkg->export_fail(@failed);
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foreach $sym (@failed) {
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require Carp;
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Carp::carp(qq["$sym" is not implemented by the $pkg module ],
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"on this architecture");
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}
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if (@failed) {
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require Carp;
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Carp::croak("Can't continue after import errors");
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}
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}
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}
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warn "Importing into $callpkg from $pkg: ",
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join(", ",sort @imports) if $Verbose;
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foreach $sym (@imports) {
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# shortcut for the common case of no type character
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(*{"${callpkg}::$sym"} = \&{"${pkg}::$sym"}, next)
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unless $sym =~ s/^(\W)//;
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$type = $1;
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*{"${callpkg}::$sym"} =
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$type eq '&' ? \&{"${pkg}::$sym"} :
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$type eq '$' ? \${"${pkg}::$sym"} :
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$type eq '@' ? \@{"${pkg}::$sym"} :
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$type eq '%' ? \%{"${pkg}::$sym"} :
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$type eq '*' ? *{"${pkg}::$sym"} :
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do { require Carp; Carp::croak("Can't export symbol: $type$sym") };
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}
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}
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sub export_to_level
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{
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my $pkg = shift;
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my ($level, $junk) = (shift, shift); # need to get rid of first arg
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# we know it already.
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my $callpkg = caller($level);
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$pkg->export($callpkg, @_);
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}
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sub import {
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my $pkg = shift;
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my $callpkg = caller($ExportLevel);
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export $pkg, $callpkg, @_;
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}
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# Utility functions
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sub _push_tags {
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my($pkg, $var, $syms) = @_;
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my $nontag;
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*export_tags = \%{"${pkg}::EXPORT_TAGS"};
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push(@{"${pkg}::$var"},
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map { $export_tags{$_} ? @{$export_tags{$_}} : scalar(++$nontag,$_) }
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(@$syms) ? @$syms : keys %export_tags);
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if ($nontag and $^W) {
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# This may change to a die one day
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require Carp;
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Carp::carp("Some names are not tags");
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}
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}
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sub export_tags { _push_tags((caller)[0], "EXPORT", \@_) }
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sub export_ok_tags { _push_tags((caller)[0], "EXPORT_OK", \@_) }
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# Default methods
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sub export_fail {
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my $self = shift;
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@_;
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}
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sub require_version {
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my($self, $wanted) = @_;
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my $pkg = ref $self || $self;
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my $version = ${"${pkg}::VERSION"};
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if (!$version or $version < $wanted) {
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$version ||= "(undef)";
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my $file = $INC{"$pkg.pm"};
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$file &&= " ($file)";
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require Carp;
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Carp::croak("$pkg $wanted required--this is only version $version$file")
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}
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$version;
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}
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1;
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# A simple self test harness. Change 'require Carp' to 'use Carp ()' for testing.
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# package main; eval(join('',<DATA>)) or die $@ unless caller;
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__END__
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package Test;
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$INC{'Exporter.pm'} = 1;
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@ISA = qw(Exporter);
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@EXPORT = qw(A1 A2 A3 A4 A5);
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@EXPORT_OK = qw(B1 B2 B3 B4 B5);
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%EXPORT_TAGS = (T1=>[qw(A1 A2 B1 B2)], T2=>[qw(A1 A2 B3 B4)], T3=>[qw(X3)]);
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@EXPORT_FAIL = qw(B4);
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Exporter::export_ok_tags('T3', 'unknown_tag');
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sub export_fail {
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map { "Test::$_" } @_ # edit symbols just as an example
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}
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package main;
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$Exporter::Verbose = 1;
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#import Test;
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#import Test qw(X3); # export ok via export_ok_tags()
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#import Test qw(:T1 !A2 /5/ !/3/ B5);
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import Test qw(:T2 !B4);
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import Test qw(:T2); # should fail
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1;
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=head1 NAME
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Exporter - Implements default import method for modules
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=head1 SYNOPSIS
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In module ModuleName.pm:
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package ModuleName;
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require Exporter;
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@ISA = qw(Exporter);
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@EXPORT = qw(...); # symbols to export by default
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@EXPORT_OK = qw(...); # symbols to export on request
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%EXPORT_TAGS = tag => [...]; # define names for sets of symbols
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In other files which wish to use ModuleName:
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use ModuleName; # import default symbols into my package
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use ModuleName qw(...); # import listed symbols into my package
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use ModuleName (); # do not import any symbols
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=head1 DESCRIPTION
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The Exporter module implements a default C<import> method which
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many modules choose to inherit rather than implement their own.
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Perl automatically calls the C<import> method when processing a
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C<use> statement for a module. Modules and C<use> are documented
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in L<perlfunc> and L<perlmod>. Understanding the concept of
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modules and how the C<use> statement operates is important to
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understanding the Exporter.
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=head2 Selecting What To Export
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Do B<not> export method names!
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Do B<not> export anything else by default without a good reason!
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Exports pollute the namespace of the module user. If you must export
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try to use @EXPORT_OK in preference to @EXPORT and avoid short or
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common symbol names to reduce the risk of name clashes.
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Generally anything not exported is still accessible from outside the
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module using the ModuleName::item_name (or $blessed_ref-E<gt>method)
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syntax. By convention you can use a leading underscore on names to
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informally indicate that they are 'internal' and not for public use.
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(It is actually possible to get private functions by saying:
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my $subref = sub { ... };
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&$subref;
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But there's no way to call that directly as a method, since a method
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must have a name in the symbol table.)
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As a general rule, if the module is trying to be object oriented
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then export nothing. If it's just a collection of functions then
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@EXPORT_OK anything but use @EXPORT with caution.
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Other module design guidelines can be found in L<perlmod>.
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=head2 Specialised Import Lists
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If the first entry in an import list begins with !, : or / then the
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list is treated as a series of specifications which either add to or
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delete from the list of names to import. They are processed left to
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right. Specifications are in the form:
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[!]name This name only
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[!]:DEFAULT All names in @EXPORT
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[!]:tag All names in $EXPORT_TAGS{tag} anonymous list
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[!]/pattern/ All names in @EXPORT and @EXPORT_OK which match
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A leading ! indicates that matching names should be deleted from the
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list of names to import. If the first specification is a deletion it
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is treated as though preceded by :DEFAULT. If you just want to import
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extra names in addition to the default set you will still need to
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include :DEFAULT explicitly.
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e.g., Module.pm defines:
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@EXPORT = qw(A1 A2 A3 A4 A5);
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@EXPORT_OK = qw(B1 B2 B3 B4 B5);
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%EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]);
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Note that you cannot use tags in @EXPORT or @EXPORT_OK.
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Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK.
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An application using Module can say something like:
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use Module qw(:DEFAULT :T2 !B3 A3);
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Other examples include:
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use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET);
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use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/);
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Remember that most patterns (using //) will need to be anchored
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with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>.
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You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the
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specifications are being processed and what is actually being imported
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into modules.
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=head2 Exporting without using Export's import method
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Exporter has a special method, 'export_to_level' which is used in situations
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where you can't directly call Export's import method. The export_to_level
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method looks like:
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MyPackage->export_to_level($where_to_export, @what_to_export);
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where $where_to_export is an integer telling how far up the calling stack
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to export your symbols, and @what_to_export is an array telling what
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symbols *to* export (usually this is @_).
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For example, suppose that you have a module, A, which already has an
|
||
|
|
import function:
|
||
|
|
|
||
|
|
package A;
|
||
|
|
|
||
|
|
@ISA = qw(Exporter);
|
||
|
|
@EXPORT_OK = qw ($b);
|
||
|
|
|
||
|
|
sub import
|
||
|
|
{
|
||
|
|
$A::b = 1; # not a very useful import method
|
||
|
|
}
|
||
|
|
|
||
|
|
and you want to Export symbol $A::b back to the module that called
|
||
|
|
package A. Since Exporter relies on the import method to work, via
|
||
|
|
inheritance, as it stands Exporter::import() will never get called.
|
||
|
|
Instead, say the following:
|
||
|
|
|
||
|
|
package A;
|
||
|
|
@ISA = qw(Exporter);
|
||
|
|
@EXPORT_OK = qw ($b);
|
||
|
|
|
||
|
|
sub import
|
||
|
|
{
|
||
|
|
$A::b = 1;
|
||
|
|
A->export_to_level(1, @_);
|
||
|
|
}
|
||
|
|
|
||
|
|
This will export the symbols one level 'above' the current package - ie: to
|
||
|
|
the program or module that used package A.
|
||
|
|
|
||
|
|
Note: Be careful not to modify '@_' at all before you call export_to_level
|
||
|
|
- or people using your package will get very unexplained results!
|
||
|
|
|
||
|
|
|
||
|
|
=head2 Module Version Checking
|
||
|
|
|
||
|
|
The Exporter module will convert an attempt to import a number from a
|
||
|
|
module into a call to $module_name-E<gt>require_version($value). This can
|
||
|
|
be used to validate that the version of the module being used is
|
||
|
|
greater than or equal to the required version.
|
||
|
|
|
||
|
|
The Exporter module supplies a default require_version method which
|
||
|
|
checks the value of $VERSION in the exporting module.
|
||
|
|
|
||
|
|
Since the default require_version method treats the $VERSION number as
|
||
|
|
a simple numeric value it will regard version 1.10 as lower than
|
||
|
|
1.9. For this reason it is strongly recommended that you use numbers
|
||
|
|
with at least two decimal places, e.g., 1.09.
|
||
|
|
|
||
|
|
=head2 Managing Unknown Symbols
|
||
|
|
|
||
|
|
In some situations you may want to prevent certain symbols from being
|
||
|
|
exported. Typically this applies to extensions which have functions
|
||
|
|
or constants that may not exist on some systems.
|
||
|
|
|
||
|
|
The names of any symbols that cannot be exported should be listed
|
||
|
|
in the C<@EXPORT_FAIL> array.
|
||
|
|
|
||
|
|
If a module attempts to import any of these symbols the Exporter
|
||
|
|
will give the module an opportunity to handle the situation before
|
||
|
|
generating an error. The Exporter will call an export_fail method
|
||
|
|
with a list of the failed symbols:
|
||
|
|
|
||
|
|
@failed_symbols = $module_name->export_fail(@failed_symbols);
|
||
|
|
|
||
|
|
If the export_fail method returns an empty list then no error is
|
||
|
|
recorded and all the requested symbols are exported. If the returned
|
||
|
|
list is not empty then an error is generated for each symbol and the
|
||
|
|
export fails. The Exporter provides a default export_fail method which
|
||
|
|
simply returns the list unchanged.
|
||
|
|
|
||
|
|
Uses for the export_fail method include giving better error messages
|
||
|
|
for some symbols and performing lazy architectural checks (put more
|
||
|
|
symbols into @EXPORT_FAIL by default and then take them out if someone
|
||
|
|
actually tries to use them and an expensive check shows that they are
|
||
|
|
usable on that platform).
|
||
|
|
|
||
|
|
=head2 Tag Handling Utility Functions
|
||
|
|
|
||
|
|
Since the symbols listed within %EXPORT_TAGS must also appear in either
|
||
|
|
@EXPORT or @EXPORT_OK, two utility functions are provided which allow
|
||
|
|
you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK:
|
||
|
|
|
||
|
|
%EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]);
|
||
|
|
|
||
|
|
Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT
|
||
|
|
Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK
|
||
|
|
|
||
|
|
Any names which are not tags are added to @EXPORT or @EXPORT_OK
|
||
|
|
unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags
|
||
|
|
names being silently added to @EXPORT or @EXPORT_OK. Future versions
|
||
|
|
may make this a fatal error.
|
||
|
|
|
||
|
|
=cut
|