Commit | Line | Data |
---|---|---|
8990e307 | 1 | package AutoLoader; |
21c92a1d | 2 | |
1be0b951 | 3 | use vars qw(@EXPORT @EXPORT_OK); |
f06db76b | 4 | |
adaafad2 GS |
5 | my $is_dosish; |
6 | my $is_vms; | |
7 | ||
1be0b951 CS |
8 | BEGIN { |
9 | require Exporter; | |
10 | @EXPORT = (); | |
11 | @EXPORT_OK = qw(AUTOLOAD); | |
adaafad2 GS |
12 | $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32'; |
13 | $is_vms = $^O eq 'VMS'; | |
1be0b951 | 14 | } |
f06db76b | 15 | |
8990e307 | 16 | AUTOLOAD { |
5a556d17 NIS |
17 | my $name; |
18 | # Braces used to preserve $1 et al. | |
19 | { | |
adaafad2 GS |
20 | # Try to find the autoloaded file from the package-qualified |
21 | # name of the sub. e.g., if the sub needed is | |
22 | # Getopt::Long::GetOptions(), then $INC{Getopt/Long.pm} is | |
23 | # something like '/usr/lib/perl5/Getopt/Long.pm', and the | |
24 | # autoload file is '/usr/lib/perl5/auto/Getopt/Long/GetOptions.al'. | |
25 | # | |
26 | # However, if @INC is a relative path, this might not work. If, | |
27 | # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is | |
28 | # 'lib/Getopt/Long.pm', and we want to require | |
29 | # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib'). | |
30 | # In this case, we simple prepend the 'auto/' and let the | |
31 | # C<require> take care of the searching for us. | |
32 | ||
33 | my ($pkg,$func) = $AUTOLOAD =~ /(.*)::([^:]+)$/; | |
34 | $pkg =~ s#::#/#g; | |
35 | if (defined($name=$INC{"$pkg.pm"})) { | |
36 | $name =~ s#^(.*)$pkg\.pm$#$1auto/$pkg/$func.al#; | |
37 | ||
38 | # if the file exists, then make sure that it is a | |
39 | # a fully anchored path (i.e either '/usr/lib/auto/foo/bar.al', | |
40 | # or './lib/auto/foo/bar.al'. This avoids C<require> searching | |
41 | # (and failing) to find the 'lib/auto/foo/bar.al' because it | |
42 | # looked for 'lib/lib/auto/foo/bar.al', given @INC = ('lib'). | |
43 | ||
44 | if (-r $name) { | |
45 | unless ($name =~ m|^/|) { | |
46 | if ($is_dosish) { | |
47 | unless ($name =~ m{^([a-z]:)?[\\/]}i) { | |
48 | $name = "./$name"; | |
49 | } | |
50 | } | |
51 | elsif ($is_vms) { | |
52 | # XXX todo by VMSmiths | |
53 | $name = "./$name"; | |
54 | } | |
55 | else { | |
56 | $name = "./$name"; | |
57 | } | |
58 | } | |
59 | } | |
60 | else { | |
61 | $name = undef; | |
62 | } | |
63 | } | |
64 | unless (defined $name) { | |
65 | # let C<require> do the searching | |
66 | $name = "auto/$AUTOLOAD.al"; | |
67 | $name =~ s#::#/#g; | |
68 | } | |
5a556d17 | 69 | } |
e14baed2 | 70 | my $save = $@; |
adaafad2 | 71 | eval { local $SIG{__DIE__}; require $name }; |
8990e307 | 72 | if ($@) { |
e14baed2 | 73 | if (substr($AUTOLOAD,-9) eq '::DESTROY') { |
4633a7c4 | 74 | *$AUTOLOAD = sub {}; |
e14baed2 | 75 | } else { |
76 | # The load might just have failed because the filename was too | |
77 | # long for some old SVR3 systems which treat long names as errors. | |
78 | # If we can succesfully truncate a long name then it's worth a go. | |
79 | # There is a slight risk that we could pick up the wrong file here | |
80 | # but autosplit should have warned about that when splitting. | |
81 | if ($name =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){ | |
720cbd86 | 82 | eval {local $SIG{__DIE__};require $name}; |
e14baed2 | 83 | } |
84 | if ($@){ | |
85 | $@ =~ s/ at .*\n//; | |
fb73857a | 86 | my $error = $@; |
87 | require Carp; | |
88 | Carp::croak($error); | |
e14baed2 | 89 | } |
a0d0e21e | 90 | } |
8990e307 | 91 | } |
e14baed2 | 92 | $@ = $save; |
8990e307 LW |
93 | goto &$AUTOLOAD; |
94 | } | |
1be0b951 | 95 | |
c2960299 | 96 | sub import { |
1be0b951 CS |
97 | my $pkg = shift; |
98 | my $callpkg = caller; | |
99 | ||
100 | # | |
101 | # Export symbols, but not by accident of inheritance. | |
102 | # | |
103 | ||
104 | Exporter::export $pkg, $callpkg, @_ if $pkg eq 'AutoLoader'; | |
105 | ||
106 | # | |
c2960299 AD |
107 | # Try to find the autosplit index file. Eg., if the call package |
108 | # is POSIX, then $INC{POSIX.pm} is something like | |
109 | # '/usr/local/lib/perl5/POSIX.pm', and the autosplit index file is in | |
110 | # '/usr/local/lib/perl5/auto/POSIX/autosplit.ix', so we require that. | |
111 | # | |
112 | # However, if @INC is a relative path, this might not work. If, | |
113 | # for example, @INC = ('lib'), then | |
114 | # $INC{POSIX.pm} is 'lib/POSIX.pm', and we want to require | |
115 | # 'auto/POSIX/autosplit.ix' (without the leading 'lib'). | |
116 | # | |
1be0b951 | 117 | |
1c1c7f20 | 118 | (my $calldir = $callpkg) =~ s#::#/#g; |
1be0b951 CS |
119 | my $path = $INC{$calldir . '.pm'}; |
120 | if (defined($path)) { | |
c2960299 | 121 | # Try absolute path name. |
1be0b951 | 122 | $path =~ s#^(.*)$calldir\.pm$#$1auto/$calldir/autosplit.ix#; |
c2960299 AD |
123 | eval { require $path; }; |
124 | # If that failed, try relative path with normal @INC searching. | |
125 | if ($@) { | |
1be0b951 | 126 | $path ="auto/$calldir/autosplit.ix"; |
c2960299 AD |
127 | eval { require $path; }; |
128 | } | |
fb73857a | 129 | if ($@) { |
130 | my $error = $@; | |
131 | require Carp; | |
132 | Carp::carp($error); | |
133 | } | |
f06db76b | 134 | } |
f06db76b | 135 | } |
8990e307 LW |
136 | |
137 | 1; | |
1be0b951 CS |
138 | |
139 | __END__ | |
140 | ||
141 | =head1 NAME | |
142 | ||
143 | AutoLoader - load subroutines only on demand | |
144 | ||
145 | =head1 SYNOPSIS | |
146 | ||
147 | package Foo; | |
148 | use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine | |
149 | ||
150 | package Bar; | |
151 | use AutoLoader; # don't import AUTOLOAD, define our own | |
152 | sub AUTOLOAD { | |
153 | ... | |
154 | $AutoLoader::AUTOLOAD = "..."; | |
155 | goto &AutoLoader::AUTOLOAD; | |
156 | } | |
157 | ||
158 | =head1 DESCRIPTION | |
159 | ||
160 | The B<AutoLoader> module works with the B<AutoSplit> module and the | |
161 | C<__END__> token to defer the loading of some subroutines until they are | |
162 | used rather than loading them all at once. | |
163 | ||
164 | To use B<AutoLoader>, the author of a module has to place the | |
165 | definitions of subroutines to be autoloaded after an C<__END__> token. | |
166 | (See L<perldata>.) The B<AutoSplit> module can then be run manually to | |
167 | extract the definitions into individual files F<auto/funcname.al>. | |
168 | ||
169 | B<AutoLoader> implements an AUTOLOAD subroutine. When an undefined | |
170 | subroutine in is called in a client module of B<AutoLoader>, | |
171 | B<AutoLoader>'s AUTOLOAD subroutine attempts to locate the subroutine in a | |
172 | file with a name related to the location of the file from which the | |
173 | client module was read. As an example, if F<POSIX.pm> is located in | |
174 | F</usr/local/lib/perl5/POSIX.pm>, B<AutoLoader> will look for perl | |
175 | subroutines B<POSIX> in F</usr/local/lib/perl5/auto/POSIX/*.al>, where | |
176 | the C<.al> file has the same name as the subroutine, sans package. If | |
177 | such a file exists, AUTOLOAD will read and evaluate it, | |
178 | thus (presumably) defining the needed subroutine. AUTOLOAD will then | |
179 | C<goto> the newly defined subroutine. | |
180 | ||
181 | Once this process completes for a given funtion, it is defined, so | |
182 | future calls to the subroutine will bypass the AUTOLOAD mechanism. | |
183 | ||
184 | =head2 Subroutine Stubs | |
185 | ||
186 | In order for object method lookup and/or prototype checking to operate | |
187 | correctly even when methods have not yet been defined it is necessary to | |
188 | "forward declare" each subroutine (as in C<sub NAME;>). See | |
189 | L<perlsub/"SYNOPSIS">. Such forward declaration creates "subroutine | |
190 | stubs", which are place holders with no code. | |
191 | ||
192 | The AutoSplit and B<AutoLoader> modules automate the creation of forward | |
193 | declarations. The AutoSplit module creates an 'index' file containing | |
194 | forward declarations of all the AutoSplit subroutines. When the | |
195 | AutoLoader module is 'use'd it loads these declarations into its callers | |
196 | package. | |
197 | ||
198 | Because of this mechanism it is important that B<AutoLoader> is always | |
199 | C<use>d and not C<require>d. | |
200 | ||
201 | =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine | |
202 | ||
203 | In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must> | |
204 | explicitly import it: | |
205 | ||
206 | use AutoLoader 'AUTOLOAD'; | |
207 | ||
208 | =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine | |
209 | ||
210 | Some modules, mainly extensions, provide their own AUTOLOAD subroutines. | |
211 | They typically need to check for some special cases (such as constants) | |
212 | and then fallback to B<AutoLoader>'s AUTOLOAD for the rest. | |
213 | ||
214 | Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine. | |
215 | Instead, they should define their own AUTOLOAD subroutines along these | |
216 | lines: | |
217 | ||
218 | use AutoLoader; | |
fb73857a | 219 | use Carp; |
1be0b951 CS |
220 | |
221 | sub AUTOLOAD { | |
222 | my $constname; | |
223 | ($constname = $AUTOLOAD) =~ s/.*:://; | |
224 | my $val = constant($constname, @_ ? $_[0] : 0); | |
225 | if ($! != 0) { | |
226 | if ($! =~ /Invalid/) { | |
227 | $AutoLoader::AUTOLOAD = $AUTOLOAD; | |
228 | goto &AutoLoader::AUTOLOAD; | |
229 | } | |
230 | else { | |
231 | croak "Your vendor has not defined constant $constname"; | |
232 | } | |
233 | } | |
fb73857a | 234 | *$AUTOLOAD = sub { $val }; # same as: eval "sub $AUTOLOAD { $val }"; |
1be0b951 CS |
235 | goto &$AUTOLOAD; |
236 | } | |
237 | ||
238 | If any module's own AUTOLOAD subroutine has no need to fallback to the | |
239 | AutoLoader's AUTOLOAD subroutine (because it doesn't have any AutoSplit | |
240 | subroutines), then that module should not use B<AutoLoader> at all. | |
241 | ||
242 | =head2 Package Lexicals | |
243 | ||
244 | Package lexicals declared with C<my> in the main block of a package | |
245 | using B<AutoLoader> will not be visible to auto-loaded subroutines, due to | |
246 | the fact that the given scope ends at the C<__END__> marker. A module | |
247 | using such variables as package globals will not work properly under the | |
248 | B<AutoLoader>. | |
249 | ||
250 | The C<vars> pragma (see L<perlmod/"vars">) may be used in such | |
251 | situations as an alternative to explicitly qualifying all globals with | |
252 | the package namespace. Variables pre-declared with this pragma will be | |
253 | visible to any autoloaded routines (but will not be invisible outside | |
254 | the package, unfortunately). | |
255 | ||
256 | =head2 B<AutoLoader> vs. B<SelfLoader> | |
257 | ||
258 | The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the | |
259 | loading of subroutines. | |
260 | ||
261 | B<SelfLoader> uses the C<__DATA__> marker rather than C<__END__>. | |
262 | While this avoids the use of a hierarchy of disk files and the | |
263 | associated open/close for each routine loaded, B<SelfLoader> suffers a | |
264 | startup speed disadvantage in the one-time parsing of the lines after | |
265 | C<__DATA__>, after which routines are cached. B<SelfLoader> can also | |
266 | handle multiple packages in a file. | |
267 | ||
268 | B<AutoLoader> only reads code as it is requested, and in many cases | |
269 | should be faster, but requires a machanism like B<AutoSplit> be used to | |
270 | create the individual files. L<ExtUtils::MakeMaker> will invoke | |
271 | B<AutoSplit> automatically if B<AutoLoader> is used in a module source | |
272 | file. | |
273 | ||
274 | =head1 CAVEATS | |
275 | ||
276 | AutoLoaders prior to Perl 5.002 had a slightly different interface. Any | |
277 | old modules which use B<AutoLoader> should be changed to the new calling | |
278 | style. Typically this just means changing a require to a use, adding | |
279 | the explicit C<'AUTOLOAD'> import if needed, and removing B<AutoLoader> | |
280 | from C<@ISA>. | |
281 | ||
282 | On systems with restrictions on file name length, the file corresponding | |
283 | to a subroutine may have a shorter name that the routine itself. This | |
284 | can lead to conflicting file names. The I<AutoSplit> package warns of | |
285 | these potential conflicts when used to split a module. | |
286 | ||
adaafad2 GS |
287 | AutoLoader may fail to find the autosplit files (or even find the wrong |
288 | ones) in cases where C<@INC> contains relative paths, B<and> the program | |
289 | does C<chdir>. | |
290 | ||
1be0b951 CS |
291 | =head1 SEE ALSO |
292 | ||
293 | L<SelfLoader> - an autoloader that doesn't use external files. | |
294 | ||
295 | =cut |