4 our(@EXPORT, @EXPORT_OK, $VERSION);
11 @EXPORT = @EXPORT = ();
12 @EXPORT_OK = @EXPORT_OK = qw(AUTOLOAD);
13 $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32';
14 $is_vms = $^O eq 'VMS';
21 # Braces used to preserve $1 et al.
23 # Try to find the autoloaded file from the package-qualified
24 # name of the sub. e.g., if the sub needed is
25 # Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is
26 # something like '/usr/lib/perl5/Getopt/Long.pm', and the
27 # autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'.
29 # However, if @INC is a relative path, this might not work. If,
30 # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is
31 # 'lib/Getopt/Long.pm', and we want to require
32 # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib').
33 # In this case, we simple prepend the 'auto/' and let the
34 # C<require> take care of the searching for us.
36 my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/);
38 if (defined($filename = $INC{"$pkg.pm"})) {
39 $filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s;
41 # if the file exists, then make sure that it is a
42 # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al',
43 # or './lib/auto/foo/bar.al'. This avoids C<require> searching
44 # (and failing) to find the 'lib/auto/foo/bar.al' because it
45 # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib').
48 unless ($filename =~ m|^/|s) {
50 unless ($filename =~ m{^([a-z]:)?[\\/]}is) {
51 $filename = "./$filename";
55 # XXX todo by VMSmiths
56 $filename = "./$filename";
59 $filename = "./$filename";
67 unless (defined $filename) {
68 # let C<require> do the searching
69 $filename = "auto/$sub.al";
70 $filename =~ s#::#/#g;
74 eval { local $SIG{__DIE__}; require $filename };
76 if (substr($sub,-9) eq '::DESTROY') {
79 # The load might just have failed because the filename was too
80 # long for some old SVR3 systems which treat long names as errors.
81 # If we can succesfully truncate a long name then it's worth a go.
82 # There is a slight risk that we could pick up the wrong file here
83 # but autosplit should have warned about that when splitting.
84 if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
85 eval { local $SIG{__DIE__}; require $filename };
101 my $callpkg = caller;
104 # Export symbols, but not by accident of inheritance.
107 if ($pkg eq 'AutoLoader') {
108 local $Exporter::ExportLevel = 1;
109 Exporter::import $pkg, @_;
113 # Try to find the autosplit index file. Eg., if the call package
114 # is POSIX, then $INC{POSIX.pm} is something like
115 # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
116 # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
118 # However, if @INC is a relative path, this might not work. If,
119 # for example, @INC = ('lib'), then
120 # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
121 # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
124 (my $calldir = $callpkg) =~ s#::#/#g;
125 my $path = $INC{$calldir . '.pm'};
126 if (defined($path)) {
127 # Try absolute path name.
128 $path =~ s#^(.*)$calldir\.pm$#$1auto/$calldir/autosplit.ix#;
129 eval { require $path; };
130 # If that failed, try relative path with normal @INC searching.
132 $path ="auto/$calldir/autosplit.ix";
133 eval { require $path; };
144 my $callpkg = caller;
145 eval "package $callpkg; sub AUTOLOAD;";
154 AutoLoader - load subroutines only on demand
159 use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
162 use AutoLoader; # don't import AUTOLOAD, define our own
165 $AutoLoader::AUTOLOAD = "...";
166 goto &AutoLoader::AUTOLOAD;
171 The B<AutoLoader> module works with the B<AutoSplit> module and the
172 C<__END__> token to defer the loading of some subroutines until they are
173 used rather than loading them all at once.
175 To use B<AutoLoader>, the author of a module has to place the
176 definitions of subroutines to be autoloaded after an C<__END__> token.
177 (See L<perldata>.) The B<AutoSplit> module can then be run manually to
178 extract the definitions into individual files F<auto/funcname.al>.
180 B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
181 subroutine in is called in a client module of B<AutoLoader>,
182 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
183 file with a name related to the location of the file from which the
184 client module was read. As an example, if F<POSIX.pm> is located in
185 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
186 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
187 the C<.al> file has the same name as the subroutine, sans package. If
188 such a file exists, AUTOLOAD will read and evaluate it,
189 thus (presumably) defining the needed subroutine. AUTOLOAD will then
190 C<goto> the newly defined subroutine.
192 Once this process completes for a given function, it is defined, so
193 future calls to the subroutine will bypass the AUTOLOAD mechanism.
195 =head2 Subroutine Stubs
197 In order for object method lookup and/or prototype checking to operate
198 correctly even when methods have not yet been defined it is necessary to
199 "forward declare" each subroutine (as in C<sub NAME;>). See
200 L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
201 stubs", which are place holders with no code.
203 The AutoSplit and B<AutoLoader> modules automate the creation of forward
204 declarations. The AutoSplit module creates an 'index' file containing
205 forward declarations of all the AutoSplit subroutines. When the
206 AutoLoader module is 'use'd it loads these declarations into its callers
209 Because of this mechanism it is important that B<AutoLoader> is always
210 C<use>d and not C<require>d.
212 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
214 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
215 explicitly import it:
217 use AutoLoader 'AUTOLOAD';
219 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
221 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
222 They typically need to check for some special cases (such as constants)
223 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
225 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
226 Instead, they should define their own AUTOLOAD subroutines along these
234 (my $constname = $sub) =~ s/.*:://;
235 my $val = constant($constname, @_ ? $_[0] : 0);
237 if ($! =~ /Invalid/ || $!{EINVAL}) {
238 $AutoLoader::AUTOLOAD = $sub;
239 goto &AutoLoader::AUTOLOAD;
242 croak "Your vendor has not defined constant $constname";
245 *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
249 If any module's own AUTOLOAD subroutine has no need to fallback to the
250 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
251 subroutines), then that module should not use B<AutoLoader> at all.
253 =head2 Package Lexicals
255 Package lexicals declared with C<my> in the main block of a package
256 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
257 the fact that the given scope ends at the C<__END__> marker. A module
258 using such variables as package globals will not work properly under the
261 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
262 situations as an alternative to explicitly qualifying all globals with
263 the package namespace. Variables pre-declared with this pragma will be
264 visible to any autoloaded routines (but will not be invisible outside
265 the package, unfortunately).
267 =head2 Not Using AutoLoader
269 You can stop using AutoLoader by simply
273 =head2 B<AutoLoader> vs. B<SelfLoader>
275 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
276 loading of subroutines.
278 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
279 While this avoids the use of a hierarchy of disk files and the
280 associated open/close for each routine loaded, B<SelfLoader> suffers a
281 startup speed disadvantage in the one-time parsing of the lines after
282 C<__DATA__>, after which routines are cached. B<SelfLoader> can also
283 handle multiple packages in a file.
285 B<AutoLoader> only reads code as it is requested, and in many cases
286 should be faster, but requires a mechanism like B<AutoSplit> be used to
287 create the individual files. L<ExtUtils::MakeMaker> will invoke
288 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
293 AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
294 old modules which use B<AutoLoader> should be changed to the new calling
295 style. Typically this just means changing a require to a use, adding
296 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
299 On systems with restrictions on file name length, the file corresponding
300 to a subroutine may have a shorter name that the routine itself. This
301 can lead to conflicting file names. The I<AutoSplit> package warns of
302 these potential conflicts when used to split a module.
304 AutoLoader may fail to find the autosplit files (or even find the wrong
305 ones) in cases where C<@INC> contains relative paths, B<and> the program
310 L<SelfLoader> - an autoloader that doesn't use external files.