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 local $!; # Do not munge the value.
92 eval { local $SIG{__DIE__}; require $filename };
94 if (substr($sub,-9) eq '::DESTROY') {
97 # The load might just have failed because the filename was too
98 # long for some old SVR3 systems which treat long names as errors.
99 # If we can succesfully truncate a long name then it's worth a go.
100 # There is a slight risk that we could pick up the wrong file here
101 # but autosplit should have warned about that when splitting.
102 if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
103 eval { local $SIG{__DIE__}; require $filename };
119 my $callpkg = caller;
122 # Export symbols, but not by accident of inheritance.
125 if ($pkg eq 'AutoLoader') {
126 local $Exporter::ExportLevel = 1;
127 Exporter::import $pkg, @_;
131 # Try to find the autosplit index file. Eg., if the call package
132 # is POSIX, then $INC{POSIX.pm} is something like
133 # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
134 # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
136 # However, if @INC is a relative path, this might not work. If,
137 # for example, @INC = ('lib'), then
138 # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
139 # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
142 (my $calldir = $callpkg) =~ s#::#/#g;
143 my $path = $INC{$calldir . '.pm'};
144 if (defined($path)) {
145 # Try absolute path name.
146 $path =~ s#^(.*)$calldir\.pm$#$1auto/$calldir/autosplit.ix#;
147 eval { require $path; };
148 # If that failed, try relative path with normal @INC searching.
150 $path ="auto/$calldir/autosplit.ix";
151 eval { require $path; };
162 my $callpkg = caller;
163 eval "package $callpkg; sub AUTOLOAD;";
172 AutoLoader - load subroutines only on demand
177 use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
180 use AutoLoader; # don't import AUTOLOAD, define our own
183 $AutoLoader::AUTOLOAD = "...";
184 goto &AutoLoader::AUTOLOAD;
189 The B<AutoLoader> module works with the B<AutoSplit> module and the
190 C<__END__> token to defer the loading of some subroutines until they are
191 used rather than loading them all at once.
193 To use B<AutoLoader>, the author of a module has to place the
194 definitions of subroutines to be autoloaded after an C<__END__> token.
195 (See L<perldata>.) The B<AutoSplit> module can then be run manually to
196 extract the definitions into individual files F<auto/funcname.al>.
198 B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
199 subroutine in is called in a client module of B<AutoLoader>,
200 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
201 file with a name related to the location of the file from which the
202 client module was read. As an example, if F<POSIX.pm> is located in
203 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
204 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
205 the C<.al> file has the same name as the subroutine, sans package. If
206 such a file exists, AUTOLOAD will read and evaluate it,
207 thus (presumably) defining the needed subroutine. AUTOLOAD will then
208 C<goto> the newly defined subroutine.
210 Once this process completes for a given function, it is defined, so
211 future calls to the subroutine will bypass the AUTOLOAD mechanism.
213 =head2 Subroutine Stubs
215 In order for object method lookup and/or prototype checking to operate
216 correctly even when methods have not yet been defined it is necessary to
217 "forward declare" each subroutine (as in C<sub NAME;>). See
218 L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
219 stubs", which are place holders with no code.
221 The AutoSplit and B<AutoLoader> modules automate the creation of forward
222 declarations. The AutoSplit module creates an 'index' file containing
223 forward declarations of all the AutoSplit subroutines. When the
224 AutoLoader module is 'use'd it loads these declarations into its callers
227 Because of this mechanism it is important that B<AutoLoader> is always
228 C<use>d and not C<require>d.
230 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
232 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
233 explicitly import it:
235 use AutoLoader 'AUTOLOAD';
237 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
239 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
240 They typically need to check for some special cases (such as constants)
241 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
243 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
244 Instead, they should define their own AUTOLOAD subroutines along these
252 (my $constname = $sub) =~ s/.*:://;
253 my $val = constant($constname, @_ ? $_[0] : 0);
255 if ($! =~ /Invalid/ || $!{EINVAL}) {
256 $AutoLoader::AUTOLOAD = $sub;
257 goto &AutoLoader::AUTOLOAD;
260 croak "Your vendor has not defined constant $constname";
263 *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
267 If any module's own AUTOLOAD subroutine has no need to fallback to the
268 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
269 subroutines), then that module should not use B<AutoLoader> at all.
271 =head2 Package Lexicals
273 Package lexicals declared with C<my> in the main block of a package
274 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
275 the fact that the given scope ends at the C<__END__> marker. A module
276 using such variables as package globals will not work properly under the
279 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
280 situations as an alternative to explicitly qualifying all globals with
281 the package namespace. Variables pre-declared with this pragma will be
282 visible to any autoloaded routines (but will not be invisible outside
283 the package, unfortunately).
285 =head2 Not Using AutoLoader
287 You can stop using AutoLoader by simply
291 =head2 B<AutoLoader> vs. B<SelfLoader>
293 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
294 loading of subroutines.
296 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
297 While this avoids the use of a hierarchy of disk files and the
298 associated open/close for each routine loaded, B<SelfLoader> suffers a
299 startup speed disadvantage in the one-time parsing of the lines after
300 C<__DATA__>, after which routines are cached. B<SelfLoader> can also
301 handle multiple packages in a file.
303 B<AutoLoader> only reads code as it is requested, and in many cases
304 should be faster, but requires a mechanism like B<AutoSplit> be used to
305 create the individual files. L<ExtUtils::MakeMaker> will invoke
306 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
311 AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
312 old modules which use B<AutoLoader> should be changed to the new calling
313 style. Typically this just means changing a require to a use, adding
314 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
317 On systems with restrictions on file name length, the file corresponding
318 to a subroutine may have a shorter name that the routine itself. This
319 can lead to conflicting file names. The I<AutoSplit> package warns of
320 these potential conflicts when used to split a module.
322 AutoLoader may fail to find the autosplit files (or even find the wrong
323 ones) in cases where C<@INC> contains relative paths, B<and> the program
328 L<SelfLoader> - an autoloader that doesn't use external files.