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';
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 $filename = "./$filename";
64 unless ($filename =~ m{^([a-z?]:)?[\\/]}is) {
65 $filename = "./$filename";
68 # XXX todo by VMSmiths
69 $filename = "./$filename";
72 $filename = "./$filename";
80 unless (defined $filename) {
81 # let C<require> do the searching
82 $filename = "auto/$sub.al";
83 $filename =~ s#::#/#g;
87 eval { local $SIG{__DIE__}; require $filename };
89 if (substr($sub,-9) eq '::DESTROY') {
92 # The load might just have failed because the filename was too
93 # long for some old SVR3 systems which treat long names as errors.
94 # If we can succesfully truncate a long name then it's worth a go.
95 # There is a slight risk that we could pick up the wrong file here
96 # but autosplit should have warned about that when splitting.
97 if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
98 eval { local $SIG{__DIE__}; require $filename };
114 my $callpkg = caller;
117 # Export symbols, but not by accident of inheritance.
120 if ($pkg eq 'AutoLoader') {
121 local $Exporter::ExportLevel = 1;
122 Exporter::import $pkg, @_;
126 # Try to find the autosplit index file. Eg., if the call package
127 # is POSIX, then $INC{POSIX.pm} is something like
128 # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
129 # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
131 # However, if @INC is a relative path, this might not work. If,
132 # for example, @INC = ('lib'), then
133 # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
134 # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
137 (my $calldir = $callpkg) =~ s#::#/#g;
138 my $path = $INC{$calldir . '.pm'};
139 if (defined($path)) {
140 # Try absolute path name.
141 $path =~ s#^(.*)$calldir\.pm$#$1auto/$calldir/autosplit.ix#;
142 eval { require $path; };
143 # If that failed, try relative path with normal @INC searching.
145 $path ="auto/$calldir/autosplit.ix";
146 eval { require $path; };
157 my $callpkg = caller;
158 eval "package $callpkg; sub AUTOLOAD;";
167 AutoLoader - load subroutines only on demand
172 use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
175 use AutoLoader; # don't import AUTOLOAD, define our own
178 $AutoLoader::AUTOLOAD = "...";
179 goto &AutoLoader::AUTOLOAD;
184 The B<AutoLoader> module works with the B<AutoSplit> module and the
185 C<__END__> token to defer the loading of some subroutines until they are
186 used rather than loading them all at once.
188 To use B<AutoLoader>, the author of a module has to place the
189 definitions of subroutines to be autoloaded after an C<__END__> token.
190 (See L<perldata>.) The B<AutoSplit> module can then be run manually to
191 extract the definitions into individual files F<auto/funcname.al>.
193 B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
194 subroutine in is called in a client module of B<AutoLoader>,
195 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
196 file with a name related to the location of the file from which the
197 client module was read. As an example, if F<POSIX.pm> is located in
198 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
199 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
200 the C<.al> file has the same name as the subroutine, sans package. If
201 such a file exists, AUTOLOAD will read and evaluate it,
202 thus (presumably) defining the needed subroutine. AUTOLOAD will then
203 C<goto> the newly defined subroutine.
205 Once this process completes for a given function, it is defined, so
206 future calls to the subroutine will bypass the AUTOLOAD mechanism.
208 =head2 Subroutine Stubs
210 In order for object method lookup and/or prototype checking to operate
211 correctly even when methods have not yet been defined it is necessary to
212 "forward declare" each subroutine (as in C<sub NAME;>). See
213 L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
214 stubs", which are place holders with no code.
216 The AutoSplit and B<AutoLoader> modules automate the creation of forward
217 declarations. The AutoSplit module creates an 'index' file containing
218 forward declarations of all the AutoSplit subroutines. When the
219 AutoLoader module is 'use'd it loads these declarations into its callers
222 Because of this mechanism it is important that B<AutoLoader> is always
223 C<use>d and not C<require>d.
225 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
227 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
228 explicitly import it:
230 use AutoLoader 'AUTOLOAD';
232 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
234 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
235 They typically need to check for some special cases (such as constants)
236 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
238 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
239 Instead, they should define their own AUTOLOAD subroutines along these
247 (my $constname = $sub) =~ s/.*:://;
248 my $val = constant($constname, @_ ? $_[0] : 0);
250 if ($! =~ /Invalid/ || $!{EINVAL}) {
251 $AutoLoader::AUTOLOAD = $sub;
252 goto &AutoLoader::AUTOLOAD;
255 croak "Your vendor has not defined constant $constname";
258 *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
262 If any module's own AUTOLOAD subroutine has no need to fallback to the
263 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
264 subroutines), then that module should not use B<AutoLoader> at all.
266 =head2 Package Lexicals
268 Package lexicals declared with C<my> in the main block of a package
269 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
270 the fact that the given scope ends at the C<__END__> marker. A module
271 using such variables as package globals will not work properly under the
274 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
275 situations as an alternative to explicitly qualifying all globals with
276 the package namespace. Variables pre-declared with this pragma will be
277 visible to any autoloaded routines (but will not be invisible outside
278 the package, unfortunately).
280 =head2 Not Using AutoLoader
282 You can stop using AutoLoader by simply
286 =head2 B<AutoLoader> vs. B<SelfLoader>
288 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
289 loading of subroutines.
291 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
292 While this avoids the use of a hierarchy of disk files and the
293 associated open/close for each routine loaded, B<SelfLoader> suffers a
294 startup speed disadvantage in the one-time parsing of the lines after
295 C<__DATA__>, after which routines are cached. B<SelfLoader> can also
296 handle multiple packages in a file.
298 B<AutoLoader> only reads code as it is requested, and in many cases
299 should be faster, but requires a mechanism like B<AutoSplit> be used to
300 create the individual files. L<ExtUtils::MakeMaker> will invoke
301 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
306 AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
307 old modules which use B<AutoLoader> should be changed to the new calling
308 style. Typically this just means changing a require to a use, adding
309 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
312 On systems with restrictions on file name length, the file corresponding
313 to a subroutine may have a shorter name that the routine itself. This
314 can lead to conflicting file names. The I<AutoSplit> package warns of
315 these potential conflicts when used to split a module.
317 AutoLoader may fail to find the autosplit files (or even find the wrong
318 ones) in cases where C<@INC> contains relative paths, B<and> the program
323 L<SelfLoader> - an autoloader that doesn't use external files.