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1 | package AutoLoader; |
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2 | |
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3 | # use vars qw(@EXPORT @EXPORT_OK $VERSION); |
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4 | |
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5 | my $is_dosish; |
6 | my $is_vms; |
7 | |
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8 | BEGIN { |
9 | require Exporter; |
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10 | @EXPORT = @EXPORT = (); |
11 | @EXPORT_OK = @EXPORT_OK = qw(AUTOLOAD); |
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12 | $is_dosish = $^O eq 'dos' || $^O eq 'os2' || $^O eq 'MSWin32'; |
13 | $is_vms = $^O eq 'VMS'; |
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14 | $VERSION = '5.57'; |
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15 | } |
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16 | |
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17 | AUTOLOAD { |
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18 | my $sub = $AUTOLOAD; |
19 | my $filename; |
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20 | # Braces used to preserve $1 et al. |
21 | { |
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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'. |
27 | # |
28 | # However, if @INC is a relative path, this might not work. If, |
29 | # for example, @INC = ('lib'), then $INC{Getopt/Long.pm} is |
30 | # 'lib/Getopt/Long.pm', and we want to require |
31 | # 'auto/Getopt/Long/GetOptions.al' (without the leading 'lib'). |
32 | # In this case, we simple prepend the 'auto/' and let the |
33 | # C<require> take care of the searching for us. |
34 | |
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35 | my ($pkg,$func) = ($sub =~ /(.*)::([^:]+)$/); |
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36 | $pkg =~ s#::#/#g; |
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37 | if (defined($filename = $INC{"$pkg.pm"})) { |
38 | $filename =~ s#^(.*)$pkg\.pm$#$1auto/$pkg/$func.al#; |
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39 | |
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'). |
45 | |
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46 | if (-r $filename) { |
47 | unless ($filename =~ m|^/|) { |
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48 | if ($is_dosish) { |
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49 | unless ($filename =~ m{^([a-z]:)?[\\/]}i) { |
50 | $filename = "./$filename"; |
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51 | } |
52 | } |
53 | elsif ($is_vms) { |
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54 | # XXX todo by VMSmiths |
55 | $filename = "./$filename"; |
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56 | } |
57 | else { |
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58 | $filename = "./$filename"; |
adaafad2 |
59 | } |
60 | } |
61 | } |
62 | else { |
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63 | $filename = undef; |
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64 | } |
65 | } |
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66 | unless (defined $filename) { |
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67 | # let C<require> do the searching |
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68 | $filename = "auto/$sub.al"; |
69 | $filename =~ s#::#/#g; |
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70 | } |
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71 | } |
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72 | my $save = $@; |
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73 | eval { local $SIG{__DIE__}; require $filename }; |
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74 | if ($@) { |
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75 | if (substr($sub,-9) eq '::DESTROY') { |
76 | *$sub = sub {}; |
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77 | } else { |
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. |
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83 | if ($filename =~ s/(\w{12,})\.al$/substr($1,0,11).".al"/e){ |
84 | eval { local $SIG{__DIE__}; require $filename }; |
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85 | } |
86 | if ($@){ |
87 | $@ =~ s/ at .*\n//; |
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88 | my $error = $@; |
89 | require Carp; |
90 | Carp::croak($error); |
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91 | } |
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92 | } |
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93 | } |
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94 | $@ = $save; |
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95 | goto &$sub; |
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96 | } |
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97 | |
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98 | sub import { |
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99 | my $pkg = shift; |
100 | my $callpkg = caller; |
101 | |
102 | # |
103 | # Export symbols, but not by accident of inheritance. |
104 | # |
105 | |
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106 | if ($pkg eq 'AutoLoader') { |
107 | local $Exporter::ExportLevel = 1; |
108 | Exporter::import $pkg, @_; |
109 | } |
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110 | |
111 | # |
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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. |
116 | # |
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'). |
121 | # |
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122 | |
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123 | (my $calldir = $callpkg) =~ s#::#/#g; |
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124 | my $path = $INC{$calldir . '.pm'}; |
125 | if (defined($path)) { |
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126 | # Try absolute path name. |
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127 | $path =~ s#^(.*)$calldir\.pm$#$1auto/$calldir/autosplit.ix#; |
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128 | eval { require $path; }; |
129 | # If that failed, try relative path with normal @INC searching. |
130 | if ($@) { |
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131 | $path ="auto/$calldir/autosplit.ix"; |
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132 | eval { require $path; }; |
133 | } |
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134 | if ($@) { |
135 | my $error = $@; |
136 | require Carp; |
137 | Carp::carp($error); |
138 | } |
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139 | } |
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140 | } |
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141 | |
142 | 1; |
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143 | |
144 | __END__ |
145 | |
146 | =head1 NAME |
147 | |
148 | AutoLoader - load subroutines only on demand |
149 | |
150 | =head1 SYNOPSIS |
151 | |
152 | package Foo; |
153 | use AutoLoader 'AUTOLOAD'; # import the default AUTOLOAD subroutine |
154 | |
155 | package Bar; |
156 | use AutoLoader; # don't import AUTOLOAD, define our own |
157 | sub AUTOLOAD { |
158 | ... |
159 | $AutoLoader::AUTOLOAD = "..."; |
160 | goto &AutoLoader::AUTOLOAD; |
161 | } |
162 | |
163 | =head1 DESCRIPTION |
164 | |
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. |
168 | |
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>. |
173 | |
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. |
185 | |
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186 | Once this process completes for a given function, it is defined, so |
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187 | future calls to the subroutine will bypass the AUTOLOAD mechanism. |
188 | |
189 | =head2 Subroutine Stubs |
190 | |
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. |
196 | |
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 |
201 | package. |
202 | |
203 | Because of this mechanism it is important that B<AutoLoader> is always |
204 | C<use>d and not C<require>d. |
205 | |
206 | =head2 Using B<AutoLoader>'s AUTOLOAD Subroutine |
207 | |
208 | In order to use B<AutoLoader>'s AUTOLOAD subroutine you I<must> |
209 | explicitly import it: |
210 | |
211 | use AutoLoader 'AUTOLOAD'; |
212 | |
213 | =head2 Overriding B<AutoLoader>'s AUTOLOAD Subroutine |
214 | |
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. |
218 | |
219 | Such modules should I<not> import B<AutoLoader>'s AUTOLOAD subroutine. |
220 | Instead, they should define their own AUTOLOAD subroutines along these |
221 | lines: |
222 | |
223 | use AutoLoader; |
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224 | use Carp; |
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225 | |
226 | sub AUTOLOAD { |
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227 | my $sub = $AUTOLOAD; |
228 | (my $constname = $sub) =~ s/.*:://; |
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229 | my $val = constant($constname, @_ ? $_[0] : 0); |
230 | if ($! != 0) { |
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231 | if ($! =~ /Invalid/ || $!{EINVAL}) { |
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232 | $AutoLoader::AUTOLOAD = $sub; |
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233 | goto &AutoLoader::AUTOLOAD; |
234 | } |
235 | else { |
236 | croak "Your vendor has not defined constant $constname"; |
237 | } |
238 | } |
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239 | *$sub = sub { $val }; # same as: eval "sub $sub { $val }"; |
240 | goto &$sub; |
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241 | } |
242 | |
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. |
246 | |
247 | =head2 Package Lexicals |
248 | |
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 |
253 | B<AutoLoader>. |
254 | |
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). |
260 | |
261 | =head2 B<AutoLoader> vs. B<SelfLoader> |
262 | |
263 | The B<AutoLoader> is similar in purpose to B<SelfLoader>: both delay the |
264 | loading of subroutines. |
265 | |
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. |
272 | |
273 | B<AutoLoader> only reads code as it is requested, and in many cases |
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274 | should be faster, but requires a mechanism like B<AutoSplit> be used to |
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275 | create the individual files. L<ExtUtils::MakeMaker> will invoke |
276 | B<AutoSplit> automatically if B<AutoLoader> is used in a module source |
277 | file. |
278 | |
279 | =head1 CAVEATS |
280 | |
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> |
285 | from C<@ISA>. |
286 | |
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. |
291 | |
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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 |
294 | does C<chdir>. |
295 | |
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296 | =head1 SEE ALSO |
297 | |
298 | L<SelfLoader> - an autoloader that doesn't use external files. |
299 | |
300 | =cut |