3 use vars qw(@EXPORT @EXPORT_OK $VERSION);
11 @EXPORT_OK = qw(AUTOLOAD);
12 $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32';
13 $is_vms = $^O eq 'VMS';
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 Exporter::export $pkg, $callpkg, @_ if $pkg eq 'AutoLoader';
109 # Try to find the autosplit index file. Eg., if the call package
110 # is POSIX, then $INC{POSIX.pm} is something like
111 # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in
112 # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that.
114 # However, if @INC is a relative path, this might not work. If,
115 # for example, @INC = ('lib'), then
116 # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require
117 # 'auto/POSIX/autosplit.ix' (without the leading 'lib').
120 (my $calldir = $callpkg) =~ s#::#/#g;
121 my $path = $INC{$calldir . '.pm'};
122 if (defined($path)) {
123 # Try absolute path name.
124 $path =~ s#^(.*)$calldir\.pm$#$1auto/$calldir/autosplit.ix#;
125 eval { require $path; };
126 # If that failed, try relative path with normal @INC searching.
128 $path ="auto/$calldir/autosplit.ix";
129 eval { require $path; };
145 AutoLoader - load subroutines only on demand
150 use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine
153 use AutoLoader; # don't import AUTOLOAD, define our own
156 $AutoLoader::AUTOLOAD = "...";
157 goto &AutoLoader::AUTOLOAD;
162 The B<AutoLoader> module works with the B<AutoSplit> module and the
163 C<__END__> token to defer the loading of some subroutines until they are
164 used rather than loading them all at once.
166 To use B<AutoLoader>, the author of a module has to place the
167 definitions of subroutines to be autoloaded after an C<__END__> token.
168 (See L<perldata>.) The B<AutoSplit> module can then be run manually to
169 extract the definitions into individual files F<auto/funcname.al>.
171 B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined
172 subroutine in is called in a client module of B<AutoLoader>,
173 B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a
174 file with a name related to the location of the file from which the
175 client module was read. As an example, if F<POSIX.pm> is located in
176 F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl
177 subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where
178 the C<.al> file has the same name as the subroutine, sans package. If
179 such a file exists, AUTOLOAD will read and evaluate it,
180 thus (presumably) defining the needed subroutine. AUTOLOAD will then
181 C<goto> the newly defined subroutine.
183 Once this process completes for a given function, it is defined, so
184 future calls to the subroutine will bypass the AUTOLOAD mechanism.
186 =head2 Subroutine Stubs
188 In order for object method lookup and/or prototype checking to operate
189 correctly even when methods have not yet been defined it is necessary to
190 "forward declare" each subroutine (as in C<sub NAME;>). See
191 L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine
192 stubs", which are place holders with no code.
194 The AutoSplit and B<AutoLoader> modules automate the creation of forward
195 declarations. The AutoSplit module creates an 'index' file containing
196 forward declarations of all the AutoSplit subroutines. When the
197 AutoLoader module is 'use'd it loads these declarations into its callers
200 Because of this mechanism it is important that B<AutoLoader> is always
201 C<use>d and not C<require>d.
203 =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine
205 In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must>
206 explicitly import it:
208 use AutoLoader 'AUTOLOAD';
210 =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine
212 Some modules, mainly extensions, provide their own AUTOLOAD subroutines.
213 They typically need to check for some special cases (such as constants)
214 and then fallback to B<AutoLoader>'s AUTOLOAD for the rest.
216 Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine.
217 Instead, they should define their own AUTOLOAD subroutines along these
225 (my $constname = $sub) =~ s/.*:://;
226 my $val = constant($constname, @_ ? $_[0] : 0);
228 if ($! =~ /Invalid/) {
229 $AutoLoader::AUTOLOAD = $sub;
230 goto &AutoLoader::AUTOLOAD;
233 croak "Your vendor has not defined constant $constname";
236 *$sub = sub { $val }; # same as: eval "sub $sub { $val }";
240 If any module's own AUTOLOAD subroutine has no need to fallback to the
241 AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit
242 subroutines), then that module should not use B<AutoLoader> at all.
244 =head2 Package Lexicals
246 Package lexicals declared with C<my> in the main block of a package
247 using B<AutoLoader> will not be visible to auto-loaded subroutines, due to
248 the fact that the given scope ends at the C<__END__> marker. A module
249 using such variables as package globals will not work properly under the
252 The C<vars> pragma (see L<perlmod/"vars">) may be used in such
253 situations as an alternative to explicitly qualifying all globals with
254 the package namespace. Variables pre-declared with this pragma will be
255 visible to any autoloaded routines (but will not be invisible outside
256 the package, unfortunately).
258 =head2 B<AutoLoader> vs. B<SelfLoader>
260 The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the
261 loading of subroutines.
263 B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>.
264 While this avoids the use of a hierarchy of disk files and the
265 associated open/close for each routine loaded, B<SelfLoader> suffers a
266 startup speed disadvantage in the one-time parsing of the lines after
267 C<__DATA__>, after which routines are cached. B<SelfLoader> can also
268 handle multiple packages in a file.
270 B<AutoLoader> only reads code as it is requested, and in many cases
271 should be faster, but requires a mechanism like B<AutoSplit> be used to
272 create the individual files. L<ExtUtils::MakeMaker> will invoke
273 B<AutoSplit> automatically if B<AutoLoader> is used in a module source
278 AutoLoaders prior to Perl 5.002 had a slightly different interface. Any
279 old modules which use B<AutoLoader> should be changed to the new calling
280 style. Typically this just means changing a require to a use, adding
281 the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader>
284 On systems with restrictions on file name length, the file corresponding
285 to a subroutine may have a shorter name that the routine itself. This
286 can lead to conflicting file names. The I<AutoSplit> package warns of
287 these potential conflicts when used to split a module.
289 AutoLoader may fail to find the autosplit files (or even find the wrong
290 ones) in cases where C<@INC> contains relative paths, B<and> the program
295 L<SelfLoader> - an autoloader that doesn't use external files.