4 our(@EXPORT, @EXPORT_OK, $VERSION);
12 @EXPORT = @EXPORT = ();
13 @EXPORT_OK = @EXPORT_OK = qw(AUTOLOAD);
14 $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32';
15 $is_epoc = $^O eq 'epoc';
16 $is_vms = $^O eq 'VMS';
23 # Braces used to preserve $1 et al.
25 # Try to find the autoloaded file from the package-qualified
26 # name of the sub. e.g., if the sub needed is
27 # Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is
28 # something like '/usr/lib/perl5/Getopt/Long.pm', and the
29 # autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'.
31 # However, if @INC is a relative path, this might not work. If,
32 # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is
33 # 'lib/Getopt/Long.pm', and we want to require
34 # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib').
35 # In this case, we simple prepend the 'auto/' and let the
36 # C<require> take care of the searching for us.
38 my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/);
40 if (defined($filename = $INC{"$pkg.pm"})) {
41 $filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s;
43 # if the file exists, then make sure that it is a
44 # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al',
45 # or './lib/auto/foo/bar.al'. This avoids C<require> searching
46 # (and failing) to find the 'lib/auto/foo/bar.al' because it
47 # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib').
50 unless ($filename =~ m|^/|s) {
52 unless ($filename =~ m{^([a-z]:)?[\\/]}is) {
53 $filename = "./$filename";
57 unless ($filename =~ m{^([a-z?]:)?[\\/]}is) {
58 $filename = "./$filename";
61 # XXX todo by VMSmiths
62 $filename = "./$filename";
65 $filename = "./$filename";
73 unless (defined $filename) {
74 # let C<require> do the searching
75 $filename = "auto/$sub.al";
76 $filename =~ s#::#/#g;
80 eval { local $SIG{__DIE__}; require $filename };
82 if (substr($sub,-9) eq '::DESTROY') {
85 # The load might just have failed because the filename was too
86 # long for some old SVR3 systems which treat long names as errors.
87 # If we can succesfully truncate a long name then it's worth a go.
88 # There is a slight risk that we could pick up the wrong file here
89 # but autosplit should have warned about that when splitting.
90 if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
91 eval { local $SIG{__DIE__}; require $filename };
107 my $callpkg = caller;
110 # Export symbols, but not by accident of inheritance.
113 if ($pkg eq 'AutoLoader') {
114 local $Exporter::ExportLevel = 1;
115 Exporter::import $pkg, @_;
119 # Try to find the autosplit index file. Eg., if the call package
120 # is POSIX, then $INC{POSIX.pm} is something like
121 # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
122 # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
124 # However, if @INC is a relative path, this might not work. If,
125 # for example, @INC = ('lib'), then
126 # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
127 # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
130 (my $calldir = $callpkg) =~ s#::#/#g;
131 my $path = $INC{$calldir . '.pm'};
132 if (defined($path)) {
133 # Try absolute path name.
134 $path =~ s#^(.*)$calldir\.pm$#$1auto/$calldir/autosplit.ix#;
135 eval { require $path; };
136 # If that failed, try relative path with normal @INC searching.
138 $path ="auto/$calldir/autosplit.ix";
139 eval { require $path; };
150 my $callpkg = caller;
151 eval "package $callpkg; sub AUTOLOAD;";
160 AutoLoader - load subroutines only on demand
165 use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
168 use AutoLoader; # don't import AUTOLOAD, define our own
171 $AutoLoader::AUTOLOAD = "...";
172 goto &AutoLoader::AUTOLOAD;
177 The B<AutoLoader> module works with the B<AutoSplit> module and the
178 C<__END__> token to defer the loading of some subroutines until they are
179 used rather than loading them all at once.
181 To use B<AutoLoader>, the author of a module has to place the
182 definitions of subroutines to be autoloaded after an C<__END__> token.
183 (See L<perldata>.) The B<AutoSplit> module can then be run manually to
184 extract the definitions into individual files F<auto/funcname.al>.
186 B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
187 subroutine in is called in a client module of B<AutoLoader>,
188 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
189 file with a name related to the location of the file from which the
190 client module was read. As an example, if F<POSIX.pm> is located in
191 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
192 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
193 the C<.al> file has the same name as the subroutine, sans package. If
194 such a file exists, AUTOLOAD will read and evaluate it,
195 thus (presumably) defining the needed subroutine. AUTOLOAD will then
196 C<goto> the newly defined subroutine.
198 Once this process completes for a given function, it is defined, so
199 future calls to the subroutine will bypass the AUTOLOAD mechanism.
201 =head2 Subroutine Stubs
203 In order for object method lookup and/or prototype checking to operate
204 correctly even when methods have not yet been defined it is necessary to
205 "forward declare" each subroutine (as in C<sub NAME;>). See
206 L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
207 stubs", which are place holders with no code.
209 The AutoSplit and B<AutoLoader> modules automate the creation of forward
210 declarations. The AutoSplit module creates an 'index' file containing
211 forward declarations of all the AutoSplit subroutines. When the
212 AutoLoader module is 'use'd it loads these declarations into its callers
215 Because of this mechanism it is important that B<AutoLoader> is always
216 C<use>d and not C<require>d.
218 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
220 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
221 explicitly import it:
223 use AutoLoader 'AUTOLOAD';
225 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
227 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
228 They typically need to check for some special cases (such as constants)
229 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
231 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
232 Instead, they should define their own AUTOLOAD subroutines along these
240 (my $constname = $sub) =~ s/.*:://;
241 my $val = constant($constname, @_ ? $_[0] : 0);
243 if ($! =~ /Invalid/ || $!{EINVAL}) {
244 $AutoLoader::AUTOLOAD = $sub;
245 goto &AutoLoader::AUTOLOAD;
248 croak "Your vendor has not defined constant $constname";
251 *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
255 If any module's own AUTOLOAD subroutine has no need to fallback to the
256 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
257 subroutines), then that module should not use B<AutoLoader> at all.
259 =head2 Package Lexicals
261 Package lexicals declared with C<my> in the main block of a package
262 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
263 the fact that the given scope ends at the C<__END__> marker. A module
264 using such variables as package globals will not work properly under the
267 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
268 situations as an alternative to explicitly qualifying all globals with
269 the package namespace. Variables pre-declared with this pragma will be
270 visible to any autoloaded routines (but will not be invisible outside
271 the package, unfortunately).
273 =head2 Not Using AutoLoader
275 You can stop using AutoLoader by simply
279 =head2 B<AutoLoader> vs. B<SelfLoader>
281 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
282 loading of subroutines.
284 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
285 While this avoids the use of a hierarchy of disk files and the
286 associated open/close for each routine loaded, B<SelfLoader> suffers a
287 startup speed disadvantage in the one-time parsing of the lines after
288 C<__DATA__>, after which routines are cached. B<SelfLoader> can also
289 handle multiple packages in a file.
291 B<AutoLoader> only reads code as it is requested, and in many cases
292 should be faster, but requires a mechanism like B<AutoSplit> be used to
293 create the individual files. L<ExtUtils::MakeMaker> will invoke
294 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
299 AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
300 old modules which use B<AutoLoader> should be changed to the new calling
301 style. Typically this just means changing a require to a use, adding
302 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
305 On systems with restrictions on file name length, the file corresponding
306 to a subroutine may have a shorter name that the routine itself. This
307 can lead to conflicting file names. The I<AutoSplit> package warns of
308 these potential conflicts when used to split a module.
310 AutoLoader may fail to find the autosplit files (or even find the wrong
311 ones) in cases where C<@INC> contains relative paths, B<and> the program
316 L<SelfLoader> - an autoloader that doesn't use external files.