6 our($VERSION, $AUTOLOAD);
14 $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32' || $^O eq 'NetWare';
15 $is_epoc = $^O eq 'epoc';
16 $is_vms = $^O eq 'VMS';
17 $is_macos = $^O eq 'MacOS';
24 # Braces used to preserve $1 et al.
26 # Try to find the autoloaded file from the package-qualified
27 # name of the sub. e.g., if the sub needed is
28 # Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is
29 # something like '/usr/lib/perl5/Getopt/Long.pm', and the
30 # autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'.
32 # However, if @INC is a relative path, this might not work. If,
33 # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is
34 # 'lib/Getopt/Long.pm', and we want to require
35 # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib').
36 # In this case, we simple prepend the 'auto/' and let the
37 # C<require> take care of the searching for us.
39 my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/);
41 if (defined($filename = $INC{"$pkg.pm"})) {
44 $filename =~ s#^(.*)$pkg\.pm\z#$1auto:$pkg:$func.al#s;
46 $filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s;
49 # if the file exists, then make sure that it is a
50 # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al',
51 # or './lib/auto/foo/bar.al'. This avoids C<require> searching
52 # (and failing) to find the 'lib/auto/foo/bar.al' because it
53 # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib').
56 unless ($filename =~ m|^/|s) {
58 unless ($filename =~ m{^([a-z]:)?[\\/]}is) {
59 if ($^O ne 'NetWare') {
60 $filename = "./$filename";
62 $filename = "$filename";
67 unless ($filename =~ m{^([a-z?]:)?[\\/]}is) {
68 $filename = "./$filename";
72 # XXX todo by VMSmiths
73 $filename = "./$filename";
76 $filename = "./$filename";
84 unless (defined $filename) {
85 # let C<require> do the searching
86 $filename = "auto/$sub.al";
87 $filename =~ s#::#/#g;
91 local $!; # Do not munge the value.
92 eval { local $SIG{__DIE__}; require $filename };
94 if (substr($sub,-9) eq '::DESTROY') {
98 # The load might just have failed because the filename was too
99 # long for some old SVR3 systems which treat long names as errors.
100 # If we can succesfully truncate a long name then it's worth a go.
101 # There is a slight risk that we could pick up the wrong file here
102 # but autosplit should have warned about that when splitting.
103 if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
104 eval { local $SIG{__DIE__}; require $filename };
120 my $callpkg = caller;
123 # Export symbols, but not by accident of inheritance.
126 if ($pkg eq 'AutoLoader') {
128 *{ $callpkg . '::AUTOLOAD' } = \&AUTOLOAD
129 if @_ and $_[0] =~ /^&?AUTOLOAD$/;
133 # Try to find the autosplit index file. Eg., if the call package
134 # is POSIX, then $INC{POSIX.pm} is something like
135 # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
136 # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
138 # However, if @INC is a relative path, this might not work. If,
139 # for example, @INC = ('lib'), then
140 # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
141 # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
144 (my $calldir = $callpkg) =~ s#::#/#g;
145 my $path = $INC{$calldir . '.pm'};
146 if (defined($path)) {
147 # Try absolute path name.
149 (my $malldir = $calldir) =~ tr#/#:#;
150 $path =~ s#^(.*)$malldir\.pm\z#$1auto:$malldir:autosplit.ix#s;
152 $path =~ s#^(.*)$calldir\.pm\z#$1auto/$calldir/autosplit.ix#;
155 eval { require $path; };
156 # If that failed, try relative path with normal @INC searching.
158 $path ="auto/$calldir/autosplit.ix";
159 eval { require $path; };
170 my $callpkg = caller;
173 my $symname = $callpkg . '::AUTOLOAD';
174 undef *{ $symname } if \&{ $symname } == \&AUTOLOAD;
175 *{ $symname } = \&{ $symname };
184 AutoLoader - load subroutines only on demand
189 use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
192 use AutoLoader; # don't import AUTOLOAD, define our own
195 $AutoLoader::AUTOLOAD = "...";
196 goto &AutoLoader::AUTOLOAD;
201 The B<AutoLoader> module works with the B<AutoSplit> module and the
202 C<__END__> token to defer the loading of some subroutines until they are
203 used rather than loading them all at once.
205 To use B<AutoLoader>, the author of a module has to place the
206 definitions of subroutines to be autoloaded after an C<__END__> token.
207 (See L<perldata>.) The B<AutoSplit> module can then be run manually to
208 extract the definitions into individual files F<auto/funcname.al>.
210 B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
211 subroutine in is called in a client module of B<AutoLoader>,
212 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
213 file with a name related to the location of the file from which the
214 client module was read. As an example, if F<POSIX.pm> is located in
215 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
216 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
217 the C<.al> file has the same name as the subroutine, sans package. If
218 such a file exists, AUTOLOAD will read and evaluate it,
219 thus (presumably) defining the needed subroutine. AUTOLOAD will then
220 C<goto> the newly defined subroutine.
222 Once this process completes for a given function, it is defined, so
223 future calls to the subroutine will bypass the AUTOLOAD mechanism.
225 =head2 Subroutine Stubs
227 In order for object method lookup and/or prototype checking to operate
228 correctly even when methods have not yet been defined it is necessary to
229 "forward declare" each subroutine (as in C<sub NAME;>). See
230 L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
231 stubs", which are place holders with no code.
233 The AutoSplit and B<AutoLoader> modules automate the creation of forward
234 declarations. The AutoSplit module creates an 'index' file containing
235 forward declarations of all the AutoSplit subroutines. When the
236 AutoLoader module is 'use'd it loads these declarations into its callers
239 Because of this mechanism it is important that B<AutoLoader> is always
240 C<use>d and not C<require>d.
242 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
244 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
245 explicitly import it:
247 use AutoLoader 'AUTOLOAD';
249 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
251 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
252 They typically need to check for some special cases (such as constants)
253 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
255 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
256 Instead, they should define their own AUTOLOAD subroutines along these
264 (my $constname = $sub) =~ s/.*:://;
265 my $val = constant($constname, @_ ? $_[0] : 0);
267 if ($! =~ /Invalid/ || $!{EINVAL}) {
268 $AutoLoader::AUTOLOAD = $sub;
269 goto &AutoLoader::AUTOLOAD;
272 croak "Your vendor has not defined constant $constname";
275 *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
279 If any module's own AUTOLOAD subroutine has no need to fallback to the
280 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
281 subroutines), then that module should not use B<AutoLoader> at all.
283 =head2 Package Lexicals
285 Package lexicals declared with C<my> in the main block of a package
286 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
287 the fact that the given scope ends at the C<__END__> marker. A module
288 using such variables as package globals will not work properly under the
291 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
292 situations as an alternative to explicitly qualifying all globals with
293 the package namespace. Variables pre-declared with this pragma will be
294 visible to any autoloaded routines (but will not be invisible outside
295 the package, unfortunately).
297 =head2 Not Using AutoLoader
299 You can stop using AutoLoader by simply
303 =head2 B<AutoLoader> vs. B<SelfLoader>
305 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
306 loading of subroutines.
308 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
309 While this avoids the use of a hierarchy of disk files and the
310 associated open/close for each routine loaded, B<SelfLoader> suffers a
311 startup speed disadvantage in the one-time parsing of the lines after
312 C<__DATA__>, after which routines are cached. B<SelfLoader> can also
313 handle multiple packages in a file.
315 B<AutoLoader> only reads code as it is requested, and in many cases
316 should be faster, but requires a mechanism like B<AutoSplit> be used to
317 create the individual files. L<ExtUtils::MakeMaker> will invoke
318 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
323 AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
324 old modules which use B<AutoLoader> should be changed to the new calling
325 style. Typically this just means changing a require to a use, adding
326 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
329 On systems with restrictions on file name length, the file corresponding
330 to a subroutine may have a shorter name that the routine itself. This
331 can lead to conflicting file names. The I<AutoSplit> package warns of
332 these potential conflicts when used to split a module.
334 AutoLoader may fail to find the autosplit files (or even find the wrong
335 ones) in cases where C<@INC> contains relative paths, B<and> the program
340 L<SelfLoader> - an autoloader that doesn't use external files.