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86530b38 AT |
1 | package AutoLoader; |
2 | ||
3 | use 5.006_001; | |
4 | our(@EXPORT, @EXPORT_OK, $VERSION); | |
5 | ||
6 | my $is_dosish; | |
7 | my $is_epoc; | |
8 | my $is_vms; | |
9 | my $is_macos; | |
10 | ||
11 | BEGIN { | |
12 | require Exporter; | |
13 | @EXPORT = @EXPORT = (); | |
14 | @EXPORT_OK = @EXPORT_OK = qw(AUTOLOAD); | |
15 | $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32' || $^O eq 'NetWare'; | |
16 | $is_epoc = $^O eq 'epoc'; | |
17 | $is_vms = $^O eq 'VMS'; | |
18 | $is_macos = $^O eq 'MacOS'; | |
19 | $VERSION = '5.59'; | |
20 | } | |
21 | ||
22 | AUTOLOAD { | |
23 | my $sub = $AUTOLOAD; | |
24 | my $filename; | |
25 | # Braces used to preserve $1 et al. | |
26 | { | |
27 | # Try to find the autoloaded file from the package-qualified | |
28 | # name of the sub. e.g., if the sub needed is | |
29 | # Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is | |
30 | # something like '/usr/lib/perl5/Getopt/Long.pm', and the | |
31 | # autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'. | |
32 | # | |
33 | # However, if @INC is a relative path, this might not work. If, | |
34 | # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is | |
35 | # 'lib/Getopt/Long.pm', and we want to require | |
36 | # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib'). | |
37 | # In this case, we simple prepend the 'auto/' and let the | |
38 | # C<require> take care of the searching for us. | |
39 | ||
40 | my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/); | |
41 | $pkg =~ s#::#/#g; | |
42 | if (defined($filename = $INC{"$pkg.pm"})) { | |
43 | if ($is_macos) { | |
44 | $pkg =~ tr#/#:#; | |
45 | $filename =~ s#^(.*)$pkg\.pm\z#$1auto:$pkg:$func.al#s; | |
46 | } else { | |
47 | $filename =~ s#^(.*)$pkg\.pm\z#$1auto/$pkg/$func.al#s; | |
48 | } | |
49 | ||
50 | # if the file exists, then make sure that it is a | |
51 | # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al', | |
52 | # or './lib/auto/foo/bar.al'. This avoids C<require> searching | |
53 | # (and failing) to find the 'lib/auto/foo/bar.al' because it | |
54 | # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib'). | |
55 | ||
56 | if (-r $filename) { | |
57 | unless ($filename =~ m|^/|s) { | |
58 | if ($is_dosish) { | |
59 | unless ($filename =~ m{^([a-z]:)?[\\/]}is) { | |
60 | if ($^O ne 'NetWare') { | |
61 | $filename = "./$filename"; | |
62 | } else { | |
63 | $filename = "$filename"; | |
64 | } | |
65 | } | |
66 | } | |
67 | elsif ($is_epoc) { | |
68 | unless ($filename =~ m{^([a-z?]:)?[\\/]}is) { | |
69 | $filename = "./$filename"; | |
70 | } | |
71 | } | |
72 | elsif ($is_vms) { | |
73 | # XXX todo by VMSmiths | |
74 | $filename = "./$filename"; | |
75 | } | |
76 | elsif (!$is_macos) { | |
77 | $filename = "./$filename"; | |
78 | } | |
79 | } | |
80 | } | |
81 | else { | |
82 | $filename = undef; | |
83 | } | |
84 | } | |
85 | unless (defined $filename) { | |
86 | # let C<require> do the searching | |
87 | $filename = "auto/$sub.al"; | |
88 | $filename =~ s#::#/#g; | |
89 | } | |
90 | } | |
91 | my $save = $@; | |
92 | local $!; # Do not munge the value. | |
93 | eval { local $SIG{__DIE__}; require $filename }; | |
94 | if ($@) { | |
95 | if (substr($sub,-9) eq '::DESTROY') { | |
96 | *$sub = sub {}; | |
97 | } else { | |
98 | # The load might just have failed because the filename was too | |
99 | # long for some old SVR3 systems which treat long names as errors. | |
100 | # If we can succesfully truncate a long name then it's worth a go. | |
101 | # There is a slight risk that we could pick up the wrong file here | |
102 | # but autosplit should have warned about that when splitting. | |
103 | if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){ | |
104 | eval { local $SIG{__DIE__}; require $filename }; | |
105 | } | |
106 | if ($@){ | |
107 | $@ =~ s/ at .*\n//; | |
108 | my $error = $@; | |
109 | require Carp; | |
110 | Carp::croak($error); | |
111 | } | |
112 | } | |
113 | } | |
114 | $@ = $save; | |
115 | goto &$sub; | |
116 | } | |
117 | ||
118 | sub import { | |
119 | my $pkg = shift; | |
120 | my $callpkg = caller; | |
121 | ||
122 | # | |
123 | # Export symbols, but not by accident of inheritance. | |
124 | # | |
125 | ||
126 | if ($pkg eq 'AutoLoader') { | |
127 | local $Exporter::ExportLevel = 1; | |
128 | Exporter::import $pkg, @_; | |
129 | } | |
130 | ||
131 | # | |
132 | # Try to find the autosplit index file. Eg., if the call package | |
133 | # is POSIX, then $INC{POSIX.pm} is something like | |
134 | # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in | |
135 | # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that. | |
136 | # | |
137 | # However, if @INC is a relative path, this might not work. If, | |
138 | # for example, @INC = ('lib'), then | |
139 | # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require | |
140 | # 'auto/POSIX/autosplit.ix' (without the leading 'lib'). | |
141 | # | |
142 | ||
143 | (my $calldir = $callpkg) =~ s#::#/#g; | |
144 | my $path = $INC{$calldir . '.pm'}; | |
145 | if (defined($path)) { | |
146 | # Try absolute path name. | |
147 | if ($is_macos) { | |
148 | (my $malldir = $calldir) =~ tr#/#:#; | |
149 | $path =~ s#^(.*)$malldir\.pm\z#$1auto:$malldir:autosplit.ix#s; | |
150 | } else { | |
151 | $path =~ s#^(.*)$calldir\.pm\z#$1auto/$calldir/autosplit.ix#; | |
152 | } | |
153 | ||
154 | eval { require $path; }; | |
155 | # If that failed, try relative path with normal @INC searching. | |
156 | if ($@) { | |
157 | $path ="auto/$calldir/autosplit.ix"; | |
158 | eval { require $path; }; | |
159 | } | |
160 | if ($@) { | |
161 | my $error = $@; | |
162 | require Carp; | |
163 | Carp::carp($error); | |
164 | } | |
165 | } | |
166 | } | |
167 | ||
168 | sub unimport { | |
169 | my $callpkg = caller; | |
170 | eval "package $callpkg; sub AUTOLOAD;"; | |
171 | } | |
172 | ||
173 | 1; | |
174 | ||
175 | __END__ | |
176 | ||
177 | =head1 NAME | |
178 | ||
179 | AutoLoader - load subroutines only on demand | |
180 | ||
181 | =head1 SYNOPSIS | |
182 | ||
183 | package Foo; | |
184 | use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine | |
185 | ||
186 | package Bar; | |
187 | use AutoLoader; # don't import AUTOLOAD, define our own | |
188 | sub AUTOLOAD { | |
189 | ... | |
190 | $AutoLoader::AUTOLOAD = "..."; | |
191 | goto &AutoLoader::AUTOLOAD; | |
192 | } | |
193 | ||
194 | =head1 DESCRIPTION | |
195 | ||
196 | The B<AutoLoader> module works with the B<AutoSplit> module and the | |
197 | C<__END__> token to defer the loading of some subroutines until they are | |
198 | used rather than loading them all at once. | |
199 | ||
200 | To use B<AutoLoader>, the author of a module has to place the | |
201 | definitions of subroutines to be autoloaded after an C<__END__> token. | |
202 | (See L<perldata>.) The B<AutoSplit> module can then be run manually to | |
203 | extract the definitions into individual files F<auto/funcname.al>. | |
204 | ||
205 | B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined | |
206 | subroutine in is called in a client module of B<AutoLoader>, | |
207 | B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a | |
208 | file with a name related to the location of the file from which the | |
209 | client module was read. As an example, if F<POSIX.pm> is located in | |
210 | F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl | |
211 | subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where | |
212 | the C<.al> file has the same name as the subroutine, sans package. If | |
213 | such a file exists, AUTOLOAD will read and evaluate it, | |
214 | thus (presumably) defining the needed subroutine. AUTOLOAD will then | |
215 | C<goto> the newly defined subroutine. | |
216 | ||
217 | Once this process completes for a given function, it is defined, so | |
218 | future calls to the subroutine will bypass the AUTOLOAD mechanism. | |
219 | ||
220 | =head2 Subroutine Stubs | |
221 | ||
222 | In order for object method lookup and/or prototype checking to operate | |
223 | correctly even when methods have not yet been defined it is necessary to | |
224 | "forward declare" each subroutine (as in C<sub NAME;>). See | |
225 | L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine | |
226 | stubs", which are place holders with no code. | |
227 | ||
228 | The AutoSplit and B<AutoLoader> modules automate the creation of forward | |
229 | declarations. The AutoSplit module creates an 'index' file containing | |
230 | forward declarations of all the AutoSplit subroutines. When the | |
231 | AutoLoader module is 'use'd it loads these declarations into its callers | |
232 | package. | |
233 | ||
234 | Because of this mechanism it is important that B<AutoLoader> is always | |
235 | C<use>d and not C<require>d. | |
236 | ||
237 | =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine | |
238 | ||
239 | In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must> | |
240 | explicitly import it: | |
241 | ||
242 | use AutoLoader 'AUTOLOAD'; | |
243 | ||
244 | =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine | |
245 | ||
246 | Some modules, mainly extensions, provide their own AUTOLOAD subroutines. | |
247 | They typically need to check for some special cases (such as constants) | |
248 | and then fallback to B<AutoLoader>'s AUTOLOAD for the rest. | |
249 | ||
250 | Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine. | |
251 | Instead, they should define their own AUTOLOAD subroutines along these | |
252 | lines: | |
253 | ||
254 | use AutoLoader; | |
255 | use Carp; | |
256 | ||
257 | sub AUTOLOAD { | |
258 | my $sub = $AUTOLOAD; | |
259 | (my $constname = $sub) =~ s/.*:://; | |
260 | my $val = constant($constname, @_ ? $_[0] : 0); | |
261 | if ($! != 0) { | |
262 | if ($! =~ /Invalid/ || $!{EINVAL}) { | |
263 | $AutoLoader::AUTOLOAD = $sub; | |
264 | goto &AutoLoader::AUTOLOAD; | |
265 | } | |
266 | else { | |
267 | croak "Your vendor has not defined constant $constname"; | |
268 | } | |
269 | } | |
270 | *$sub = sub { $val }; # same as: eval "sub $sub { $val }"; | |
271 | goto &$sub; | |
272 | } | |
273 | ||
274 | If any module's own AUTOLOAD subroutine has no need to fallback to the | |
275 | AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit | |
276 | subroutines), then that module should not use B<AutoLoader> at all. | |
277 | ||
278 | =head2 Package Lexicals | |
279 | ||
280 | Package lexicals declared with C<my> in the main block of a package | |
281 | using B<AutoLoader> will not be visible to auto-loaded subroutines, due to | |
282 | the fact that the given scope ends at the C<__END__> marker. A module | |
283 | using such variables as package globals will not work properly under the | |
284 | B<AutoLoader>. | |
285 | ||
286 | The C<vars> pragma (see L<perlmod/"vars">) may be used in such | |
287 | situations as an alternative to explicitly qualifying all globals with | |
288 | the package namespace. Variables pre-declared with this pragma will be | |
289 | visible to any autoloaded routines (but will not be invisible outside | |
290 | the package, unfortunately). | |
291 | ||
292 | =head2 Not Using AutoLoader | |
293 | ||
294 | You can stop using AutoLoader by simply | |
295 | ||
296 | no AutoLoader; | |
297 | ||
298 | =head2 B<AutoLoader> vs. B<SelfLoader> | |
299 | ||
300 | The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the | |
301 | loading of subroutines. | |
302 | ||
303 | B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>. | |
304 | While this avoids the use of a hierarchy of disk files and the | |
305 | associated open/close for each routine loaded, B<SelfLoader> suffers a | |
306 | startup speed disadvantage in the one-time parsing of the lines after | |
307 | C<__DATA__>, after which routines are cached. B<SelfLoader> can also | |
308 | handle multiple packages in a file. | |
309 | ||
310 | B<AutoLoader> only reads code as it is requested, and in many cases | |
311 | should be faster, but requires a mechanism like B<AutoSplit> be used to | |
312 | create the individual files. L<ExtUtils::MakeMaker> will invoke | |
313 | B<AutoSplit> automatically if B<AutoLoader> is used in a module source | |
314 | file. | |
315 | ||
316 | =head1 CAVEATS | |
317 | ||
318 | AutoLoaders prior to Perl 5.002 had a slightly different interface. Any | |
319 | old modules which use B<AutoLoader> should be changed to the new calling | |
320 | style. Typically this just means changing a require to a use, adding | |
321 | the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader> | |
322 | from C<@ISA>. | |
323 | ||
324 | On systems with restrictions on file name length, the file corresponding | |
325 | to a subroutine may have a shorter name that the routine itself. This | |
326 | can lead to conflicting file names. The I<AutoSplit> package warns of | |
327 | these potential conflicts when used to split a module. | |
328 | ||
329 | AutoLoader may fail to find the autosplit files (or even find the wrong | |
330 | ones) in cases where C<@INC> contains relative paths, B<and> the program | |
331 | does C<chdir>. | |
332 | ||
333 | =head1 SEE ALSO | |
334 | ||
335 | L<SelfLoader> - an autoloader that doesn't use external files. | |
336 | ||
337 | =cut |