4 our(@EXPORT, @EXPORT_OK, $VERSION);
13 @EXPORT = @EXPORT = ();
14 @EXPORT_OK = @EXPORT_OK = qw(AUTOLOAD);
15 $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32' || $^O eq 'NetWare';
16 $is_epoc = $^O eq 'epoc';
17 $is_vms = $^O eq 'VMS';
18 $is_macos = $^O eq 'MacOS';
25 # Braces used to preserve $1 et al.
27 # Try to find the autoloaded file from the package-qualified
28 # name of the sub. e.g., if the sub needed is
29 # Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is
30 # something like '/usr/lib/perl5/Getopt/Long.pm', and the
31 # autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'.
33 # However, if @INC is a relative path, this might not work. If,
34 # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is
35 # 'lib/Getopt/Long.pm', and we want to require
36 # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib').
37 # In this case, we simple prepend the 'auto/' and let the
38 # C<require> take care of the searching for us.
40 my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/);
42 if (defined($filename = $INC{"$pkg.pm"})) {
45 $filename =~ s#^(.*)$pkg\.pm\z#$1auto:$pkg:$func.al#s;
47 $filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s;
50 # if the file exists, then make sure that it is a
51 # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al',
52 # or './lib/auto/foo/bar.al'. This avoids C<require> searching
53 # (and failing) to find the 'lib/auto/foo/bar.al' because it
54 # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib').
57 unless ($filename =~ m|^/|s) {
59 unless ($filename =~ m{^([a-z]:)?[\\/]}is) {
60 if ($^O ne 'NetWare') {
61 $filename = "./$filename";
63 $filename = "$filename";
68 unless ($filename =~ m{^([a-z?]:)?[\\/]}is) {
69 $filename = "./$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 eval { local $SIG{__DIE__}; require $filename };
93 if (substr($sub,-9) eq '::DESTROY') {
96 # The load might just have failed because the filename was too
97 # long for some old SVR3 systems which treat long names as errors.
98 # If we can succesfully truncate a long name then it's worth a go.
99 # There is a slight risk that we could pick up the wrong file here
100 # but autosplit should have warned about that when splitting.
101 if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
102 eval { local $SIG{__DIE__}; require $filename };
118 my $callpkg = caller;
121 # Export symbols, but not by accident of inheritance.
124 if ($pkg eq 'AutoLoader') {
125 local $Exporter::ExportLevel = 1;
126 Exporter::import $pkg, @_;
130 # Try to find the autosplit index file. Eg., if the call package
131 # is POSIX, then $INC{POSIX.pm} is something like
132 # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
133 # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
135 # However, if @INC is a relative path, this might not work. If,
136 # for example, @INC = ('lib'), then
137 # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
138 # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
141 (my $calldir = $callpkg) =~ s#::#/#g;
142 my $path = $INC{$calldir . '.pm'};
143 if (defined($path)) {
144 # Try absolute path name.
145 $path =~ s#^(.*)$calldir\.pm$#$1auto/$calldir/autosplit.ix#;
146 eval { require $path; };
147 # If that failed, try relative path with normal @INC searching.
149 $path ="auto/$calldir/autosplit.ix";
150 eval { require $path; };
161 my $callpkg = caller;
162 eval "package $callpkg; sub AUTOLOAD;";
171 AutoLoader - load subroutines only on demand
176 use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
179 use AutoLoader; # don't import AUTOLOAD, define our own
182 $AutoLoader::AUTOLOAD = "...";
183 goto &AutoLoader::AUTOLOAD;
188 The B<AutoLoader> module works with the B<AutoSplit> module and the
189 C<__END__> token to defer the loading of some subroutines until they are
190 used rather than loading them all at once.
192 To use B<AutoLoader>, the author of a module has to place the
193 definitions of subroutines to be autoloaded after an C<__END__> token.
194 (See L<perldata>.) The B<AutoSplit> module can then be run manually to
195 extract the definitions into individual files F<auto/funcname.al>.
197 B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
198 subroutine in is called in a client module of B<AutoLoader>,
199 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
200 file with a name related to the location of the file from which the
201 client module was read. As an example, if F<POSIX.pm> is located in
202 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
203 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
204 the C<.al> file has the same name as the subroutine, sans package. If
205 such a file exists, AUTOLOAD will read and evaluate it,
206 thus (presumably) defining the needed subroutine. AUTOLOAD will then
207 C<goto> the newly defined subroutine.
209 Once this process completes for a given function, it is defined, so
210 future calls to the subroutine will bypass the AUTOLOAD mechanism.
212 =head2 Subroutine Stubs
214 In order for object method lookup and/or prototype checking to operate
215 correctly even when methods have not yet been defined it is necessary to
216 "forward declare" each subroutine (as in C<sub NAME;>). See
217 L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
218 stubs", which are place holders with no code.
220 The AutoSplit and B<AutoLoader> modules automate the creation of forward
221 declarations. The AutoSplit module creates an 'index' file containing
222 forward declarations of all the AutoSplit subroutines. When the
223 AutoLoader module is 'use'd it loads these declarations into its callers
226 Because of this mechanism it is important that B<AutoLoader> is always
227 C<use>d and not C<require>d.
229 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
231 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
232 explicitly import it:
234 use AutoLoader 'AUTOLOAD';
236 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
238 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
239 They typically need to check for some special cases (such as constants)
240 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
242 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
243 Instead, they should define their own AUTOLOAD subroutines along these
251 (my $constname = $sub) =~ s/.*:://;
252 my $val = constant($constname, @_ ? $_[0] : 0);
254 if ($! =~ /Invalid/ || $!{EINVAL}) {
255 $AutoLoader::AUTOLOAD = $sub;
256 goto &AutoLoader::AUTOLOAD;
259 croak "Your vendor has not defined constant $constname";
262 *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
266 If any module's own AUTOLOAD subroutine has no need to fallback to the
267 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
268 subroutines), then that module should not use B<AutoLoader> at all.
270 =head2 Package Lexicals
272 Package lexicals declared with C<my> in the main block of a package
273 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
274 the fact that the given scope ends at the C<__END__> marker. A module
275 using such variables as package globals will not work properly under the
278 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
279 situations as an alternative to explicitly qualifying all globals with
280 the package namespace. Variables pre-declared with this pragma will be
281 visible to any autoloaded routines (but will not be invisible outside
282 the package, unfortunately).
284 =head2 Not Using AutoLoader
286 You can stop using AutoLoader by simply
290 =head2 B<AutoLoader> vs. B<SelfLoader>
292 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
293 loading of subroutines.
295 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
296 While this avoids the use of a hierarchy of disk files and the
297 associated open/close for each routine loaded, B<SelfLoader> suffers a
298 startup speed disadvantage in the one-time parsing of the lines after
299 C<__DATA__>, after which routines are cached. B<SelfLoader> can also
300 handle multiple packages in a file.
302 B<AutoLoader> only reads code as it is requested, and in many cases
303 should be faster, but requires a mechanism like B<AutoSplit> be used to
304 create the individual files. L<ExtUtils::MakeMaker> will invoke
305 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
310 AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
311 old modules which use B<AutoLoader> should be changed to the new calling
312 style. Typically this just means changing a require to a use, adding
313 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
316 On systems with restrictions on file name length, the file corresponding
317 to a subroutine may have a shorter name that the routine itself. This
318 can lead to conflicting file names. The I<AutoSplit> package warns of
319 these potential conflicts when used to split a module.
321 AutoLoader may fail to find the autosplit files (or even find the wrong
322 ones) in cases where C<@INC> contains relative paths, B<and> the program
327 L<SelfLoader> - an autoloader that doesn't use external files.