3 # use vars qw(@EXPORT @EXPORT_OK $VERSION);
10 @EXPORT = @EXPORT = ();
11 @EXPORT_OK = @EXPORT_OK = qw(AUTOLOAD);
12 $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32';
13 $is_vms = $^O eq 'VMS';
14 $VERSION = $VERSION = '5.57';
20 # Braces used to preserve $1 et al.
22 # Try to find the autoloaded file from the package-qualified
23 # name of the sub. e.g., if the sub needed is
24 # Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is
25 # something like '/usr/lib/perl5/Getopt/Long.pm', and the
26 # autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'.
28 # However, if @INC is a relative path, this might not work. If,
29 # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is
30 # 'lib/Getopt/Long.pm', and we want to require
31 # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib').
32 # In this case, we simple prepend the 'auto/' and let the
33 # C<require> take care of the searching for us.
35 my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/);
37 if (defined($filename = $INC{"$pkg.pm"})) {
38 $filename =~ s#^(.*)$pkg\.pm$#$1auto/$pkg/$func.al#;
40 # if the file exists, then make sure that it is a
41 # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al',
42 # or './lib/auto/foo/bar.al'. This avoids C<require> searching
43 # (and failing) to find the 'lib/auto/foo/bar.al' because it
44 # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib').
47 unless ($filename =~ m|^/|) {
49 unless ($filename =~ m{^([a-z]:)?[\\/]}i) {
50 $filename = "./$filename";
54 # XXX todo by VMSmiths
55 $filename = "./$filename";
58 $filename = "./$filename";
66 unless (defined $filename) {
67 # let C<require> do the searching
68 $filename = "auto/$sub.al";
69 $filename =~ s#::#/#g;
73 eval { local $SIG{__DIE__}; require $filename };
75 if (substr($sub,-9) eq '::DESTROY') {
78 # The load might just have failed because the filename was too
79 # long for some old SVR3 systems which treat long names as errors.
80 # If we can succesfully truncate a long name then it's worth a go.
81 # There is a slight risk that we could pick up the wrong file here
82 # but autosplit should have warned about that when splitting.
83 if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){
84 eval { local $SIG{__DIE__}; require $filename };
100 my $callpkg = caller;
103 # Export symbols, but not by accident of inheritance.
106 if ($pkg eq 'AutoLoader') {
107 local $Exporter::ExportLevel = 1;
108 Exporter::import $pkg, @_;
112 # Try to find the autosplit index file. Eg., if the call package
113 # is POSIX, then $INC{POSIX.pm} is something like
114 # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
115 # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
117 # However, if @INC is a relative path, this might not work. If,
118 # for example, @INC = ('lib'), then
119 # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
120 # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
123 (my $calldir = $callpkg) =~ s#::#/#g;
124 my $path = $INC{$calldir . '.pm'};
125 if (defined($path)) {
126 # Try absolute path name.
127 $path =~ s#^(.*)$calldir\.pm$#$1auto/$calldir/autosplit.ix#;
128 eval { require $path; };
129 # If that failed, try relative path with normal @INC searching.
131 $path ="auto/$calldir/autosplit.ix";
132 eval { require $path; };
148 AutoLoader - load subroutines only on demand
153 use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
156 use AutoLoader; # don't import AUTOLOAD, define our own
159 $AutoLoader::AUTOLOAD = "...";
160 goto &AutoLoader::AUTOLOAD;
165 The B<AutoLoader> module works with the B<AutoSplit> module and the
166 C<__END__> token to defer the loading of some subroutines until they are
167 used rather than loading them all at once.
169 To use B<AutoLoader>, the author of a module has to place the
170 definitions of subroutines to be autoloaded after an C<__END__> token.
171 (See L<perldata>.) The B<AutoSplit> module can then be run manually to
172 extract the definitions into individual files F<auto/funcname.al>.
174 B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
175 subroutine in is called in a client module of B<AutoLoader>,
176 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
177 file with a name related to the location of the file from which the
178 client module was read. As an example, if F<POSIX.pm> is located in
179 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
180 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
181 the C<.al> file has the same name as the subroutine, sans package. If
182 such a file exists, AUTOLOAD will read and evaluate it,
183 thus (presumably) defining the needed subroutine. AUTOLOAD will then
184 C<goto> the newly defined subroutine.
186 Once this process completes for a given function, it is defined, so
187 future calls to the subroutine will bypass the AUTOLOAD mechanism.
189 =head2 Subroutine Stubs
191 In order for object method lookup and/or prototype checking to operate
192 correctly even when methods have not yet been defined it is necessary to
193 "forward declare" each subroutine (as in C<sub NAME;>). See
194 L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
195 stubs", which are place holders with no code.
197 The AutoSplit and B<AutoLoader> modules automate the creation of forward
198 declarations. The AutoSplit module creates an 'index' file containing
199 forward declarations of all the AutoSplit subroutines. When the
200 AutoLoader module is 'use'd it loads these declarations into its callers
203 Because of this mechanism it is important that B<AutoLoader> is always
204 C<use>d and not C<require>d.
206 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
208 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
209 explicitly import it:
211 use AutoLoader 'AUTOLOAD';
213 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
215 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
216 They typically need to check for some special cases (such as constants)
217 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
219 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
220 Instead, they should define their own AUTOLOAD subroutines along these
228 (my $constname = $sub) =~ s/.*:://;
229 my $val = constant($constname, @_ ? $_[0] : 0);
231 if ($! =~ /Invalid/ || $!{EINVAL}) {
232 $AutoLoader::AUTOLOAD = $sub;
233 goto &AutoLoader::AUTOLOAD;
236 croak "Your vendor has not defined constant $constname";
239 *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
243 If any module's own AUTOLOAD subroutine has no need to fallback to the
244 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
245 subroutines), then that module should not use B<AutoLoader> at all.
247 =head2 Package Lexicals
249 Package lexicals declared with C<my> in the main block of a package
250 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
251 the fact that the given scope ends at the C<__END__> marker. A module
252 using such variables as package globals will not work properly under the
255 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
256 situations as an alternative to explicitly qualifying all globals with
257 the package namespace. Variables pre-declared with this pragma will be
258 visible to any autoloaded routines (but will not be invisible outside
259 the package, unfortunately).
261 =head2 B<AutoLoader> vs. B<SelfLoader>
263 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
264 loading of subroutines.
266 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
267 While this avoids the use of a hierarchy of disk files and the
268 associated open/close for each routine loaded, B<SelfLoader> suffers a
269 startup speed disadvantage in the one-time parsing of the lines after
270 C<__DATA__>, after which routines are cached. B<SelfLoader> can also
271 handle multiple packages in a file.
273 B<AutoLoader> only reads code as it is requested, and in many cases
274 should be faster, but requires a mechanism like B<AutoSplit> be used to
275 create the individual files. L<ExtUtils::MakeMaker> will invoke
276 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
281 AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
282 old modules which use B<AutoLoader> should be changed to the new calling
283 style. Typically this just means changing a require to a use, adding
284 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
287 On systems with restrictions on file name length, the file corresponding
288 to a subroutine may have a shorter name that the routine itself. This
289 can lead to conflicting file names. The I<AutoSplit> package warns of
290 these potential conflicts when used to split a module.
292 AutoLoader may fail to find the autosplit files (or even find the wrong
293 ones) in cases where C<@INC> contains relative paths, B<and> the program
298 L<SelfLoader> - an autoloader that doesn't use external files.