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920dae64 AT |
1 | package AutoLoader; |
2 | ||
3 | use strict; | |
4 | use 5.006_001; | |
5 | ||
6 | our($VERSION, $AUTOLOAD); | |
7 | ||
8 | my $is_dosish; | |
9 | my $is_epoc; | |
10 | my $is_vms; | |
11 | my $is_macos; | |
12 | ||
13 | BEGIN { | |
14 | $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32' || $^O eq 'NetWare'; | |
15 | $is_epoc = $^O eq 'epoc'; | |
16 | $is_vms = $^O eq 'VMS'; | |
17 | $is_macos = $^O eq 'MacOS'; | |
18 | $VERSION = '5.60'; | |
19 | } | |
20 | ||
21 | AUTOLOAD { | |
22 | my $sub = $AUTOLOAD; | |
23 | my $filename; | |
24 | # Braces used to preserve $1 et al. | |
25 | { | |
26 | # Try to find the autoloaded file from the package-qualified | |
27 | # name of the sub. e.g., if the sub needed is | |
28 | # Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is | |
29 | # something like '/usr/lib/perl5/Getopt/Long.pm', and the | |
30 | # autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'. | |
31 | # | |
32 | # However, if @INC is a relative path, this might not work. If, | |
33 | # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is | |
34 | # 'lib/Getopt/Long.pm', and we want to require | |
35 | # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib'). | |
36 | # In this case, we simple prepend the 'auto/' and let the | |
37 | # C<require> take care of the searching for us. | |
38 | ||
39 | my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/); | |
40 | $pkg =~ s#::#/#g; | |
41 | if (defined($filename = $INC{"$pkg.pm"})) { | |
42 | if ($is_macos) { | |
43 | $pkg =~ tr#/#:#; | |
44 | $filename =~ s#^(.*)$pkg\.pm\z#$1auto:$pkg:$func.al#s; | |
45 | } else { | |
46 | $filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s; | |
47 | } | |
48 | ||
49 | # if the file exists, then make sure that it is a | |
50 | # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al', | |
51 | # or './lib/auto/foo/bar.al'. This avoids C<require> searching | |
52 | # (and failing) to find the 'lib/auto/foo/bar.al' because it | |
53 | # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib'). | |
54 | ||
55 | if (-r $filename) { | |
56 | unless ($filename =~ m|^/|s) { | |
57 | if ($is_dosish) { | |
58 | unless ($filename =~ m{^([a-z]:)?[\\/]}is) { | |
59 | if ($^O ne 'NetWare') { | |
60 | $filename = "./$filename"; | |
61 | } else { | |
62 | $filename = "$filename"; | |
63 | } | |
64 | } | |
65 | } | |
66 | elsif ($is_epoc) { | |
67 | unless ($filename =~ m{^([a-z?]:)?[\\/]}is) { | |
68 | $filename = "./$filename"; | |
69 | } | |
70 | } | |
71 | elsif ($is_vms) { | |
72 | # XXX todo by VMSmiths | |
73 | $filename = "./$filename"; | |
74 | } | |
75 | elsif (!$is_macos) { | |
76 | $filename = "./$filename"; | |
77 | } | |
78 | } | |
79 | } | |
80 | else { | |
81 | $filename = undef; | |
82 | } | |
83 | } | |
84 | unless (defined $filename) { | |
85 | # let C<require> do the searching | |
86 | $filename = "auto/$sub.al"; | |
87 | $filename =~ s#::#/#g; | |
88 | } | |
89 | } | |
90 | my $save = $@; | |
91 | local $!; # Do not munge the value. | |
92 | eval { local $SIG{__DIE__}; require $filename }; | |
93 | if ($@) { | |
94 | if (substr($sub,-9) eq '::DESTROY') { | |
95 | no strict 'refs'; | |
96 | *$sub = sub {}; | |
97 | $@ = undef; | |
98 | } elsif ($@ =~ /^Can't locate/) { | |
99 | # The load might just have failed because the filename was too | |
100 | # long for some old SVR3 systems which treat long names as errors. | |
101 | # If we can successfully truncate a long name then it's worth a go. | |
102 | # There is a slight risk that we could pick up the wrong file here | |
103 | # but autosplit should have warned about that when splitting. | |
104 | if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){ | |
105 | eval { local $SIG{__DIE__}; require $filename }; | |
106 | } | |
107 | } | |
108 | if ($@){ | |
109 | $@ =~ s/ at .*\n//; | |
110 | my $error = $@; | |
111 | require Carp; | |
112 | Carp::croak($error); | |
113 | } | |
114 | } | |
115 | $@ = $save; | |
116 | goto &$sub; | |
117 | } | |
118 | ||
119 | sub import { | |
120 | my $pkg = shift; | |
121 | my $callpkg = caller; | |
122 | ||
123 | # | |
124 | # Export symbols, but not by accident of inheritance. | |
125 | # | |
126 | ||
127 | if ($pkg eq 'AutoLoader') { | |
128 | no strict 'refs'; | |
129 | *{ $callpkg . '::AUTOLOAD' } = \&AUTOLOAD | |
130 | if @_ and $_[0] =~ /^&?AUTOLOAD$/; | |
131 | } | |
132 | ||
133 | # | |
134 | # Try to find the autosplit index file. Eg., if the call package | |
135 | # is POSIX, then $INC{POSIX.pm} is something like | |
136 | # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in | |
137 | # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that. | |
138 | # | |
139 | # However, if @INC is a relative path, this might not work. If, | |
140 | # for example, @INC = ('lib'), then | |
141 | # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require | |
142 | # 'auto/POSIX/autosplit.ix' (without the leading 'lib'). | |
143 | # | |
144 | ||
145 | (my $calldir = $callpkg) =~ s#::#/#g; | |
146 | my $path = $INC{$calldir . '.pm'}; | |
147 | if (defined($path)) { | |
148 | # Try absolute path name. | |
149 | if ($is_macos) { | |
150 | (my $malldir = $calldir) =~ tr#/#:#; | |
151 | $path =~ s#^(.*)$malldir\.pm\z#$1auto:$malldir:autosplit.ix#s; | |
152 | } else { | |
153 | $path =~ s#^(.*)$calldir\.pm\z#$1auto/$calldir/autosplit.ix#; | |
154 | } | |
155 | ||
156 | eval { require $path; }; | |
157 | # If that failed, try relative path with normal @INC searching. | |
158 | if ($@) { | |
159 | $path ="auto/$calldir/autosplit.ix"; | |
160 | eval { require $path; }; | |
161 | } | |
162 | if ($@) { | |
163 | my $error = $@; | |
164 | require Carp; | |
165 | Carp::carp($error); | |
166 | } | |
167 | } | |
168 | } | |
169 | ||
170 | sub unimport { | |
171 | my $callpkg = caller; | |
172 | ||
173 | no strict 'refs'; | |
174 | my $symname = $callpkg . '::AUTOLOAD'; | |
175 | undef *{ $symname } if \&{ $symname } == \&AUTOLOAD; | |
176 | *{ $symname } = \&{ $symname }; | |
177 | } | |
178 | ||
179 | 1; | |
180 | ||
181 | __END__ | |
182 | ||
183 | =head1 NAME | |
184 | ||
185 | AutoLoader - load subroutines only on demand | |
186 | ||
187 | =head1 SYNOPSIS | |
188 | ||
189 | package Foo; | |
190 | use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine | |
191 | ||
192 | package Bar; | |
193 | use AutoLoader; # don't import AUTOLOAD, define our own | |
194 | sub AUTOLOAD { | |
195 | ... | |
196 | $AutoLoader::AUTOLOAD = "..."; | |
197 | goto &AutoLoader::AUTOLOAD; | |
198 | } | |
199 | ||
200 | =head1 DESCRIPTION | |
201 | ||
202 | The B<AutoLoader> module works with the B<AutoSplit> module and the | |
203 | C<__END__> token to defer the loading of some subroutines until they are | |
204 | used rather than loading them all at once. | |
205 | ||
206 | To use B<AutoLoader>, the author of a module has to place the | |
207 | definitions of subroutines to be autoloaded after an C<__END__> token. | |
208 | (See L<perldata>.) The B<AutoSplit> module can then be run manually to | |
209 | extract the definitions into individual files F<auto/funcname.al>. | |
210 | ||
211 | B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined | |
212 | subroutine in is called in a client module of B<AutoLoader>, | |
213 | B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a | |
214 | file with a name related to the location of the file from which the | |
215 | client module was read. As an example, if F<POSIX.pm> is located in | |
216 | F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl | |
217 | subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where | |
218 | the C<.al> file has the same name as the subroutine, sans package. If | |
219 | such a file exists, AUTOLOAD will read and evaluate it, | |
220 | thus (presumably) defining the needed subroutine. AUTOLOAD will then | |
221 | C<goto> the newly defined subroutine. | |
222 | ||
223 | Once this process completes for a given function, it is defined, so | |
224 | future calls to the subroutine will bypass the AUTOLOAD mechanism. | |
225 | ||
226 | =head2 Subroutine Stubs | |
227 | ||
228 | In order for object method lookup and/or prototype checking to operate | |
229 | correctly even when methods have not yet been defined it is necessary to | |
230 | "forward declare" each subroutine (as in C<sub NAME;>). See | |
231 | L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine | |
232 | stubs", which are place holders with no code. | |
233 | ||
234 | The AutoSplit and B<AutoLoader> modules automate the creation of forward | |
235 | declarations. The AutoSplit module creates an 'index' file containing | |
236 | forward declarations of all the AutoSplit subroutines. When the | |
237 | AutoLoader module is 'use'd it loads these declarations into its callers | |
238 | package. | |
239 | ||
240 | Because of this mechanism it is important that B<AutoLoader> is always | |
241 | C<use>d and not C<require>d. | |
242 | ||
243 | =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine | |
244 | ||
245 | In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must> | |
246 | explicitly import it: | |
247 | ||
248 | use AutoLoader 'AUTOLOAD'; | |
249 | ||
250 | =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine | |
251 | ||
252 | Some modules, mainly extensions, provide their own AUTOLOAD subroutines. | |
253 | They typically need to check for some special cases (such as constants) | |
254 | and then fallback to B<AutoLoader>'s AUTOLOAD for the rest. | |
255 | ||
256 | Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine. | |
257 | Instead, they should define their own AUTOLOAD subroutines along these | |
258 | lines: | |
259 | ||
260 | use AutoLoader; | |
261 | use Carp; | |
262 | ||
263 | sub AUTOLOAD { | |
264 | my $sub = $AUTOLOAD; | |
265 | (my $constname = $sub) =~ s/.*:://; | |
266 | my $val = constant($constname, @_ ? $_[0] : 0); | |
267 | if ($! != 0) { | |
268 | if ($! =~ /Invalid/ || $!{EINVAL}) { | |
269 | $AutoLoader::AUTOLOAD = $sub; | |
270 | goto &AutoLoader::AUTOLOAD; | |
271 | } | |
272 | else { | |
273 | croak "Your vendor has not defined constant $constname"; | |
274 | } | |
275 | } | |
276 | *$sub = sub { $val }; # same as: eval "sub $sub { $val }"; | |
277 | goto &$sub; | |
278 | } | |
279 | ||
280 | If any module's own AUTOLOAD subroutine has no need to fallback to the | |
281 | AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit | |
282 | subroutines), then that module should not use B<AutoLoader> at all. | |
283 | ||
284 | =head2 Package Lexicals | |
285 | ||
286 | Package lexicals declared with C<my> in the main block of a package | |
287 | using B<AutoLoader> will not be visible to auto-loaded subroutines, due to | |
288 | the fact that the given scope ends at the C<__END__> marker. A module | |
289 | using such variables as package globals will not work properly under the | |
290 | B<AutoLoader>. | |
291 | ||
292 | The C<vars> pragma (see L<perlmod/"vars">) may be used in such | |
293 | situations as an alternative to explicitly qualifying all globals with | |
294 | the package namespace. Variables pre-declared with this pragma will be | |
295 | visible to any autoloaded routines (but will not be invisible outside | |
296 | the package, unfortunately). | |
297 | ||
298 | =head2 Not Using AutoLoader | |
299 | ||
300 | You can stop using AutoLoader by simply | |
301 | ||
302 | no AutoLoader; | |
303 | ||
304 | =head2 B<AutoLoader> vs. B<SelfLoader> | |
305 | ||
306 | The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the | |
307 | loading of subroutines. | |
308 | ||
309 | B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>. | |
310 | While this avoids the use of a hierarchy of disk files and the | |
311 | associated open/close for each routine loaded, B<SelfLoader> suffers a | |
312 | startup speed disadvantage in the one-time parsing of the lines after | |
313 | C<__DATA__>, after which routines are cached. B<SelfLoader> can also | |
314 | handle multiple packages in a file. | |
315 | ||
316 | B<AutoLoader> only reads code as it is requested, and in many cases | |
317 | should be faster, but requires a mechanism like B<AutoSplit> be used to | |
318 | create the individual files. L<ExtUtils::MakeMaker> will invoke | |
319 | B<AutoSplit> automatically if B<AutoLoader> is used in a module source | |
320 | file. | |
321 | ||
322 | =head1 CAVEATS | |
323 | ||
324 | AutoLoaders prior to Perl 5.002 had a slightly different interface. Any | |
325 | old modules which use B<AutoLoader> should be changed to the new calling | |
326 | style. Typically this just means changing a require to a use, adding | |
327 | the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader> | |
328 | from C<@ISA>. | |
329 | ||
330 | On systems with restrictions on file name length, the file corresponding | |
331 | to a subroutine may have a shorter name that the routine itself. This | |
332 | can lead to conflicting file names. The I<AutoSplit> package warns of | |
333 | these potential conflicts when used to split a module. | |
334 | ||
335 | AutoLoader may fail to find the autosplit files (or even find the wrong | |
336 | ones) in cases where C<@INC> contains relative paths, B<and> the program | |
337 | does C<chdir>. | |
338 | ||
339 | =head1 SEE ALSO | |
340 | ||
341 | L<SelfLoader> - an autoloader that doesn't use external files. | |
342 | ||
343 | =cut |