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1 | package SelfLoader; |
2 | use Carp; |
3 | require Exporter; |
4 | @ISA = qw(Exporter); |
5 | @EXPORT = qw(AUTOLOAD); |
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6 | $VERSION = 1.07; sub Version {$VERSION} |
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7 | $DEBUG = 0; |
8 | |
9 | my %Cache; # private cache for all SelfLoader's client packages |
10 | |
11 | AUTOLOAD { |
12 | print STDERR "SelfLoader::AUTOLOAD for $AUTOLOAD\n" if $DEBUG; |
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13 | my $SL_code = $Cache{$AUTOLOAD}; |
14 | unless ($SL_code) { |
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15 | # Maybe this pack had stubs before __DATA__, and never initialized. |
16 | # Or, this maybe an automatic DESTROY method call when none exists. |
17 | $AUTOLOAD =~ m/^(.*)::/; |
18 | SelfLoader->_load_stubs($1) unless exists $Cache{"${1}::<DATA"}; |
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19 | $SL_code = $Cache{$AUTOLOAD}; |
20 | $SL_code = "sub $AUTOLOAD { }" |
21 | if (!$SL_code and $AUTOLOAD =~ m/::DESTROY$/); |
22 | croak "Undefined subroutine $AUTOLOAD" unless $SL_code; |
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23 | } |
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24 | print STDERR "SelfLoader::AUTOLOAD eval: $SL_code\n" if $DEBUG; |
25 | eval $SL_code; |
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26 | if ($@) { |
27 | $@ =~ s/ at .*\n//; |
28 | croak $@; |
29 | } |
30 | defined(&$AUTOLOAD) || die "SelfLoader inconsistency error"; |
31 | delete $Cache{$AUTOLOAD}; |
32 | goto &$AUTOLOAD |
33 | } |
34 | |
35 | sub load_stubs { shift->_load_stubs((caller)[0]) } |
36 | |
37 | sub _load_stubs { |
38 | my($self, $callpack) = @_; |
39 | my $fh = \*{"${callpack}::DATA"}; |
40 | my $currpack = $callpack; |
41 | my($line,$name,@lines, @stubs, $protoype); |
42 | |
43 | print STDERR "SelfLoader::load_stubs($callpack)\n" if $DEBUG; |
44 | croak("$callpack doesn't contain an __DATA__ token") |
45 | unless fileno($fh); |
46 | $Cache{"${currpack}::<DATA"} = 1; # indicate package is cached |
47 | |
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48 | while(defined($line = <$fh>) and $line !~ m/^__END__/) { |
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49 | if ($line =~ m/^sub\s+([\w:]+)\s*(\([\\\$\@\%\&\*\;]*\))?/) { |
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50 | push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype)); |
51 | $protoype = $2; |
52 | @lines = ($line); |
53 | if (index($1,'::') == -1) { # simple sub name |
54 | $name = "${currpack}::$1"; |
55 | } else { # sub name with package |
56 | $name = $1; |
57 | $name =~ m/^(.*)::/; |
58 | if (defined(&{"${1}::AUTOLOAD"})) { |
59 | \&{"${1}::AUTOLOAD"} == \&SelfLoader::AUTOLOAD || |
60 | die 'SelfLoader Error: attempt to specify Selfloading', |
61 | " sub $name in non-selfloading module $1"; |
62 | } else { |
63 | $self->export($1,'AUTOLOAD'); |
64 | } |
65 | } |
66 | } elsif ($line =~ m/^package\s+([\w:]+)/) { # A package declared |
67 | push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype)); |
68 | $self->_package_defined($line); |
69 | $name = ''; |
70 | @lines = (); |
71 | $currpack = $1; |
72 | $Cache{"${currpack}::<DATA"} = 1; # indicate package is cached |
73 | if (defined(&{"${1}::AUTOLOAD"})) { |
74 | \&{"${1}::AUTOLOAD"} == \&SelfLoader::AUTOLOAD || |
75 | die 'SelfLoader Error: attempt to specify Selfloading', |
76 | " package $currpack which already has AUTOLOAD"; |
77 | } else { |
78 | $self->export($currpack,'AUTOLOAD'); |
79 | } |
80 | } else { |
81 | push(@lines,$line); |
82 | } |
83 | } |
84 | close($fh) unless defined($line) && $line =~ /^__END__\s*DATA/; # __END__ |
85 | push(@stubs, $self->_add_to_cache($name, $currpack, \@lines, $protoype)); |
86 | eval join('', @stubs) if @stubs; |
87 | } |
88 | |
89 | |
90 | sub _add_to_cache { |
91 | my($self,$fullname,$pack,$lines, $protoype) = @_; |
92 | return () unless $fullname; |
93 | carp("Redefining sub $fullname") if exists $Cache{$fullname}; |
94 | $Cache{$fullname} = join('', "package $pack; ",@$lines); |
95 | print STDERR "SelfLoader cached $fullname: $Cache{$fullname}" if $DEBUG; |
96 | # return stub to be eval'd |
97 | defined($protoype) ? "sub $fullname $protoype;" : "sub $fullname;" |
98 | } |
99 | |
100 | sub _package_defined {} |
101 | |
102 | 1; |
103 | __END__ |
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104 | |
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105 | =head1 NAME |
106 | |
107 | SelfLoader - load functions only on demand |
108 | |
109 | =head1 SYNOPSIS |
110 | |
111 | package FOOBAR; |
112 | use SelfLoader; |
113 | |
114 | ... (initializing code) |
115 | |
116 | __DATA__ |
117 | sub {.... |
118 | |
119 | |
120 | =head1 DESCRIPTION |
121 | |
122 | This module tells its users that functions in the FOOBAR package are to be |
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123 | autoloaded from after the C<__DATA__> token. See also |
124 | L<perlsub/"Autoloading">. |
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125 | |
126 | =head2 The __DATA__ token |
127 | |
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128 | The C<__DATA__> token tells the perl compiler that the perl code |
129 | for compilation is finished. Everything after the C<__DATA__> token |
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130 | is available for reading via the filehandle FOOBAR::DATA, |
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131 | where FOOBAR is the name of the current package when the C<__DATA__> |
132 | token is reached. This works just the same as C<__END__> does in |
133 | package 'main', but for other modules data after C<__END__> is not |
134 | automatically retreivable , whereas data after C<__DATA__> is. |
135 | The C<__DATA__> token is not recognized in versions of perl prior to |
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136 | 5.001m. |
137 | |
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138 | Note that it is possible to have C<__DATA__> tokens in the same package |
139 | in multiple files, and that the last C<__DATA__> token in a given |
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140 | package that is encountered by the compiler is the one accessible |
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141 | by the filehandle. This also applies to C<__END__> and main, i.e. if |
142 | the 'main' program has an C<__END__>, but a module 'require'd (_not_ 'use'd) |
143 | by that program has a 'package main;' declaration followed by an 'C<__DATA__>', |
144 | then the C<DATA> filehandle is set to access the data after the C<__DATA__> |
145 | in the module, _not_ the data after the C<__END__> token in the 'main' |
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146 | program, since the compiler encounters the 'require'd file later. |
147 | |
148 | =head2 SelfLoader autoloading |
149 | |
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150 | The B<SelfLoader> works by the user placing the C<__DATA__> |
151 | token I<after> perl code which needs to be compiled and |
152 | run at 'require' time, but I<before> subroutine declarations |
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153 | that can be loaded in later - usually because they may never |
154 | be called. |
155 | |
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156 | The B<SelfLoader> will read from the FOOBAR::DATA filehandle to |
157 | load in the data after C<__DATA__>, and load in any subroutine |
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158 | when it is called. The costs are the one-time parsing of the |
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159 | data after C<__DATA__>, and a load delay for the _first_ |
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160 | call of any autoloaded function. The benefits (hopefully) |
161 | are a speeded up compilation phase, with no need to load |
162 | functions which are never used. |
163 | |
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164 | The B<SelfLoader> will stop reading from C<__DATA__> if |
165 | it encounters the C<__END__> token - just as you would expect. |
166 | If the C<__END__> token is present, and is followed by the |
167 | token DATA, then the B<SelfLoader> leaves the FOOBAR::DATA |
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168 | filehandle open on the line after that token. |
169 | |
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170 | The B<SelfLoader> exports the C<AUTOLOAD> subroutine to the |
171 | package using the B<SelfLoader>, and this loads the called |
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172 | subroutine when it is first called. |
173 | |
174 | There is no advantage to putting subroutines which will _always_ |
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175 | be called after the C<__DATA__> token. |
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176 | |
177 | =head2 Autoloading and package lexicals |
178 | |
179 | A 'my $pack_lexical' statement makes the variable $pack_lexical |
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180 | local _only_ to the file up to the C<__DATA__> token. Subroutines |
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181 | declared elsewhere _cannot_ see these types of variables, |
182 | just as if you declared subroutines in the package but in another |
183 | file, they cannot see these variables. |
184 | |
185 | So specifically, autoloaded functions cannot see package |
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186 | lexicals (this applies to both the B<SelfLoader> and the Autoloader). |
187 | The C<vars> pragma provides an alternative to defining package-level |
188 | globals that will be visible to autoloaded routines. See the documentation |
189 | on B<vars> in the pragma section of L<perlmod>. |
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190 | |
191 | =head2 SelfLoader and AutoLoader |
192 | |
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193 | The B<SelfLoader> can replace the AutoLoader - just change 'use AutoLoader' |
194 | to 'use SelfLoader' (though note that the B<SelfLoader> exports |
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195 | the AUTOLOAD function - but if you have your own AUTOLOAD and |
196 | are using the AutoLoader too, you probably know what you're doing), |
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197 | and the C<__END__> token to C<__DATA__>. You will need perl version 5.001m |
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198 | or later to use this (version 5.001 with all patches up to patch m). |
199 | |
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200 | There is no need to inherit from the B<SelfLoader>. |
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201 | |
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202 | The B<SelfLoader> works similarly to the AutoLoader, but picks up the |
203 | subs from after the C<__DATA__> instead of in the 'lib/auto' directory. |
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204 | There is a maintainance gain in not needing to run AutoSplit on the module |
205 | at installation, and a runtime gain in not needing to keep opening and |
206 | closing files to load subs. There is a runtime loss in needing |
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207 | to parse the code after the C<__DATA__>. Details of the B<AutoLoader> and |
208 | another view of these distinctions can be found in that module's |
209 | documentation. |
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210 | |
211 | =head2 __DATA__, __END__, and the FOOBAR::DATA filehandle. |
212 | |
213 | This section is only relevant if you want to use |
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214 | the C<FOOBAR::DATA> together with the B<SelfLoader>. |
215 | |
216 | Data after the C<__DATA__> token in a module is read using the |
217 | FOOBAR::DATA filehandle. C<__END__> can still be used to denote the end |
218 | of the C<__DATA__> section if followed by the token DATA - this is supported |
219 | by the B<SelfLoader>. The C<FOOBAR::DATA> filehandle is left open if an |
220 | C<__END__> followed by a DATA is found, with the filehandle positioned at |
221 | the start of the line after the C<__END__> token. If no C<__END__> token is |
222 | present, or an C<__END__> token with no DATA token on the same line, then |
223 | the filehandle is closed. |
224 | |
225 | The B<SelfLoader> reads from wherever the current |
226 | position of the C<FOOBAR::DATA> filehandle is, until the |
227 | EOF or C<__END__>. This means that if you want to use |
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228 | that filehandle (and ONLY if you want to), you should either |
229 | |
230 | 1. Put all your subroutine declarations immediately after |
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231 | the C<__DATA__> token and put your own data after those |
232 | declarations, using the C<__END__> token to mark the end |
233 | of subroutine declarations. You must also ensure that the B<SelfLoader> |
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234 | reads first by calling 'SelfLoader-E<gt>load_stubs();', or by using a |
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235 | function which is selfloaded; |
236 | |
237 | or |
238 | |
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239 | 2. You should read the C<FOOBAR::DATA> filehandle first, leaving |
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240 | the handle open and positioned at the first line of subroutine |
241 | declarations. |
242 | |
243 | You could conceivably do both. |
244 | |
245 | =head2 Classes and inherited methods. |
246 | |
247 | For modules which are not classes, this section is not relevant. |
248 | This section is only relevant if you have methods which could |
249 | be inherited. |
250 | |
251 | A subroutine stub (or forward declaration) looks like |
252 | |
253 | sub stub; |
254 | |
255 | i.e. it is a subroutine declaration without the body of the |
256 | subroutine. For modules which are not classes, there is no real |
257 | need for stubs as far as autoloading is concerned. |
258 | |
259 | For modules which ARE classes, and need to handle inherited methods, |
260 | stubs are needed to ensure that the method inheritance mechanism works |
261 | properly. You can load the stubs into the module at 'require' time, by |
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262 | adding the statement 'SelfLoader-E<gt>load_stubs();' to the module to do |
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263 | this. |
264 | |
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265 | The alternative is to put the stubs in before the C<__DATA__> token BEFORE |
266 | releasing the module, and for this purpose the C<Devel::SelfStubber> |
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267 | module is available. However this does require the extra step of ensuring |
268 | that the stubs are in the module. If this is done I strongly recommend |
269 | that this is done BEFORE releasing the module - it should NOT be done |
270 | at install time in general. |
271 | |
272 | =head1 Multiple packages and fully qualified subroutine names |
273 | |
274 | Subroutines in multiple packages within the same file are supported - but you |
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275 | should note that this requires exporting the C<SelfLoader::AUTOLOAD> to |
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276 | every package which requires it. This is done automatically by the |
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277 | B<SelfLoader> when it first loads the subs into the cache, but you should |
278 | really specify it in the initialization before the C<__DATA__> by putting |
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279 | a 'use SelfLoader' statement in each package. |
280 | |
281 | Fully qualified subroutine names are also supported. For example, |
282 | |
283 | __DATA__ |
284 | sub foo::bar {23} |
285 | package baz; |
286 | sub dob {32} |
287 | |
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288 | will all be loaded correctly by the B<SelfLoader>, and the B<SelfLoader> |
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289 | will ensure that the packages 'foo' and 'baz' correctly have the |
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290 | B<SelfLoader> C<AUTOLOAD> method when the data after C<__DATA__> is first |
291 | parsed. |
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292 | |
293 | =cut |