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;
171 eval "package $callpkg; sub AUTOLOAD;";
180 AutoLoader - load subroutines only on demand
185 use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
188 use AutoLoader; # don't import AUTOLOAD, define our own
191 $AutoLoader::AUTOLOAD = "...";
192 goto &AutoLoader::AUTOLOAD;
197 The B<AutoLoader> module works with the B<AutoSplit> module and the
198 C<__END__> token to defer the loading of some subroutines until they are
199 used rather than loading them all at once.
201 To use B<AutoLoader>, the author of a module has to place the
202 definitions of subroutines to be autoloaded after an C<__END__> token.
203 (See L<perldata>.) The B<AutoSplit> module can then be run manually to
204 extract the definitions into individual files F<auto/funcname.al>.
206 B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
207 subroutine in is called in a client module of B<AutoLoader>,
208 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
209 file with a name related to the location of the file from which the
210 client module was read. As an example, if F<POSIX.pm> is located in
211 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
212 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
213 the C<.al> file has the same name as the subroutine, sans package. If
214 such a file exists, AUTOLOAD will read and evaluate it,
215 thus (presumably) defining the needed subroutine. AUTOLOAD will then
216 C<goto> the newly defined subroutine.
218 Once this process completes for a given function, it is defined, so
219 future calls to the subroutine will bypass the AUTOLOAD mechanism.
221 =head2 Subroutine Stubs
223 In order for object method lookup and/or prototype checking to operate
224 correctly even when methods have not yet been defined it is necessary to
225 "forward declare" each subroutine (as in C<sub NAME;>). See
226 L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
227 stubs", which are place holders with no code.
229 The AutoSplit and B<AutoLoader> modules automate the creation of forward
230 declarations. The AutoSplit module creates an 'index' file containing
231 forward declarations of all the AutoSplit subroutines. When the
232 AutoLoader module is 'use'd it loads these declarations into its callers
235 Because of this mechanism it is important that B<AutoLoader> is always
236 C<use>d and not C<require>d.
238 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
240 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
241 explicitly import it:
243 use AutoLoader 'AUTOLOAD';
245 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
247 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
248 They typically need to check for some special cases (such as constants)
249 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
251 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
252 Instead, they should define their own AUTOLOAD subroutines along these
260 (my $constname = $sub) =~ s/.*:://;
261 my $val = constant($constname, @_ ? $_[0] : 0);
263 if ($! =~ /Invalid/ || $!{EINVAL}) {
264 $AutoLoader::AUTOLOAD = $sub;
265 goto &AutoLoader::AUTOLOAD;
268 croak "Your vendor has not defined constant $constname";
271 *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
275 If any module's own AUTOLOAD subroutine has no need to fallback to the
276 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
277 subroutines), then that module should not use B<AutoLoader> at all.
279 =head2 Package Lexicals
281 Package lexicals declared with C<my> in the main block of a package
282 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
283 the fact that the given scope ends at the C<__END__> marker. A module
284 using such variables as package globals will not work properly under the
287 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
288 situations as an alternative to explicitly qualifying all globals with
289 the package namespace. Variables pre-declared with this pragma will be
290 visible to any autoloaded routines (but will not be invisible outside
291 the package, unfortunately).
293 =head2 Not Using AutoLoader
295 You can stop using AutoLoader by simply
299 =head2 B<AutoLoader> vs. B<SelfLoader>
301 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
302 loading of subroutines.
304 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
305 While this avoids the use of a hierarchy of disk files and the
306 associated open/close for each routine loaded, B<SelfLoader> suffers a
307 startup speed disadvantage in the one-time parsing of the lines after
308 C<__DATA__>, after which routines are cached. B<SelfLoader> can also
309 handle multiple packages in a file.
311 B<AutoLoader> only reads code as it is requested, and in many cases
312 should be faster, but requires a mechanism like B<AutoSplit> be used to
313 create the individual files. L<ExtUtils::MakeMaker> will invoke
314 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
319 AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
320 old modules which use B<AutoLoader> should be changed to the new calling
321 style. Typically this just means changing a require to a use, adding
322 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
325 On systems with restrictions on file name length, the file corresponding
326 to a subroutine may have a shorter name that the routine itself. This
327 can lead to conflicting file names. The I<AutoSplit> package warns of
328 these potential conflicts when used to split a module.
330 AutoLoader may fail to find the autosplit files (or even find the wrong
331 ones) in cases where C<@INC> contains relative paths, B<and> the program
336 L<SelfLoader> - an autoloader that doesn't use external files.