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1 | package Exporter; |
2 | |
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3 | require 5.006; |
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4 | |
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5 | use strict; |
6 | no strict 'refs'; |
7 | |
8 | our $Debug = 0; |
9 | our $ExportLevel = 0; |
10 | our $Verbose ||= 0; |
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11 | our $VERSION = '5.565'; |
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12 | $Carp::Internal{Exporter} = 1; |
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13 | |
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14 | sub export_to_level { |
15 | require Exporter::Heavy; |
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16 | goto &Exporter::Heavy::heavy_export_to_level; |
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17 | } |
18 | |
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19 | sub export { |
20 | require Exporter::Heavy; |
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21 | goto &Exporter::Heavy::heavy_export; |
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22 | } |
23 | |
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24 | sub export_tags { |
25 | require Exporter::Heavy; |
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26 | Exporter::Heavy::_push_tags((caller)[0], "EXPORT", \@_); |
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27 | } |
28 | |
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29 | sub export_ok_tags { |
30 | require Exporter::Heavy; |
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31 | Exporter::Heavy::_push_tags((caller)[0], "EXPORT_OK", \@_); |
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32 | } |
33 | |
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34 | sub import { |
35 | my $pkg = shift; |
36 | my $callpkg = caller($ExportLevel); |
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37 | |
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38 | # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-( |
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39 | my($exports, $export_cache, $fail) |
40 | = (\@{"$pkg\::EXPORT"}, \%{"$pkg\::EXPORT"}, \@{"$pkg\::EXPORT_FAIL"}); |
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41 | return export $pkg, $callpkg, @_ |
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42 | if $Verbose or $Debug or @$fail > 1; |
43 | my $args = @_ or @_ = @$exports; |
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44 | |
45 | local $_; |
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46 | if ($args and not %$export_cache) { |
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47 | s/^&//, $export_cache->{$_} = 1 |
48 | foreach (@$exports, @{"$pkg\::EXPORT_OK"}); |
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49 | } |
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50 | my $heavy; |
51 | # Try very hard not to use {} and hence have to enter scope on the foreach |
52 | # We bomb out of the loop with last as soon as heavy is set. |
53 | if ($args or $fail) { |
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54 | ($heavy = (/\W/ or $args and not exists $export_cache->{$_} |
fa1bb02f |
55 | or @$fail and $_ eq $fail->[0])) and last |
56 | foreach (@_); |
57 | } else { |
58 | ($heavy = /\W/) and last |
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59 | foreach (@_); |
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60 | } |
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61 | return export $pkg, $callpkg, ($args ? @_ : ()) if $heavy; |
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62 | local $SIG{__WARN__} = |
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63 | sub {require Carp; &Carp::carp}; |
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64 | # shortcut for the common case of no type character |
65 | *{"$callpkg\::$_"} = \&{"$pkg\::$_"} foreach @_; |
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66 | } |
67 | |
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68 | |
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69 | # Default methods |
70 | |
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71 | sub export_fail { |
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72 | my $self = shift; |
73 | @_; |
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74 | } |
75 | |
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76 | |
77 | sub require_version { |
78 | require Exporter::Heavy; |
79 | goto &Exporter::Heavy::require_version; |
80 | } |
81 | |
82 | |
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83 | 1; |
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84 | __END__ |
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85 | |
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86 | =head1 NAME |
87 | |
88 | Exporter - Implements default import method for modules |
89 | |
90 | =head1 SYNOPSIS |
91 | |
92 | In module ModuleName.pm: |
93 | |
94 | package ModuleName; |
95 | require Exporter; |
96 | @ISA = qw(Exporter); |
97 | |
98 | @EXPORT = qw(...); # symbols to export by default |
99 | @EXPORT_OK = qw(...); # symbols to export on request |
100 | %EXPORT_TAGS = tag => [...]; # define names for sets of symbols |
101 | |
102 | In other files which wish to use ModuleName: |
103 | |
104 | use ModuleName; # import default symbols into my package |
105 | |
106 | use ModuleName qw(...); # import listed symbols into my package |
107 | |
108 | use ModuleName (); # do not import any symbols |
109 | |
110 | =head1 DESCRIPTION |
111 | |
112 | The Exporter module implements a default C<import> method which |
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113 | many modules choose to inherit rather than implement their own. |
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114 | |
115 | Perl automatically calls the C<import> method when processing a |
116 | C<use> statement for a module. Modules and C<use> are documented |
117 | in L<perlfunc> and L<perlmod>. Understanding the concept of |
118 | modules and how the C<use> statement operates is important to |
119 | understanding the Exporter. |
120 | |
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121 | =head2 How to Export |
122 | |
123 | The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of |
124 | symbols that are going to be exported into the users name space by |
125 | default, or which they can request to be exported, respectively. The |
126 | symbols can represent functions, scalars, arrays, hashes, or typeglobs. |
127 | The symbols must be given by full name with the exception that the |
128 | ampersand in front of a function is optional, e.g. |
129 | |
130 | @EXPORT = qw(afunc $scalar @array); # afunc is a function |
131 | @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc |
132 | |
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133 | =head2 Selecting What To Export |
134 | |
135 | Do B<not> export method names! |
136 | |
137 | Do B<not> export anything else by default without a good reason! |
138 | |
139 | Exports pollute the namespace of the module user. If you must export |
140 | try to use @EXPORT_OK in preference to @EXPORT and avoid short or |
141 | common symbol names to reduce the risk of name clashes. |
142 | |
143 | Generally anything not exported is still accessible from outside the |
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144 | module using the ModuleName::item_name (or $blessed_ref-E<gt>method) |
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145 | syntax. By convention you can use a leading underscore on names to |
146 | informally indicate that they are 'internal' and not for public use. |
147 | |
148 | (It is actually possible to get private functions by saying: |
149 | |
150 | my $subref = sub { ... }; |
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151 | $subref->(@args); # Call it as a function |
152 | $obj->$subref(@args); # Use it as a method |
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153 | |
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154 | However if you use them for methods it is up to you to figure out |
155 | how to make inheritance work.) |
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156 | |
157 | As a general rule, if the module is trying to be object oriented |
158 | then export nothing. If it's just a collection of functions then |
159 | @EXPORT_OK anything but use @EXPORT with caution. |
160 | |
161 | Other module design guidelines can be found in L<perlmod>. |
162 | |
163 | =head2 Specialised Import Lists |
164 | |
165 | If the first entry in an import list begins with !, : or / then the |
166 | list is treated as a series of specifications which either add to or |
167 | delete from the list of names to import. They are processed left to |
168 | right. Specifications are in the form: |
169 | |
170 | [!]name This name only |
171 | [!]:DEFAULT All names in @EXPORT |
172 | [!]:tag All names in $EXPORT_TAGS{tag} anonymous list |
173 | [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match |
174 | |
175 | A leading ! indicates that matching names should be deleted from the |
176 | list of names to import. If the first specification is a deletion it |
177 | is treated as though preceded by :DEFAULT. If you just want to import |
178 | extra names in addition to the default set you will still need to |
179 | include :DEFAULT explicitly. |
180 | |
181 | e.g., Module.pm defines: |
182 | |
183 | @EXPORT = qw(A1 A2 A3 A4 A5); |
184 | @EXPORT_OK = qw(B1 B2 B3 B4 B5); |
185 | %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]); |
186 | |
187 | Note that you cannot use tags in @EXPORT or @EXPORT_OK. |
188 | Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK. |
189 | |
190 | An application using Module can say something like: |
191 | |
192 | use Module qw(:DEFAULT :T2 !B3 A3); |
193 | |
194 | Other examples include: |
195 | |
196 | use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET); |
197 | use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/); |
198 | |
199 | Remember that most patterns (using //) will need to be anchored |
200 | with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>. |
201 | |
202 | You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the |
203 | specifications are being processed and what is actually being imported |
204 | into modules. |
205 | |
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206 | =head2 Exporting without using Export's import method |
207 | |
208 | Exporter has a special method, 'export_to_level' which is used in situations |
209 | where you can't directly call Export's import method. The export_to_level |
210 | method looks like: |
211 | |
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212 | MyPackage->export_to_level($where_to_export, $package, @what_to_export); |
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213 | |
214 | where $where_to_export is an integer telling how far up the calling stack |
215 | to export your symbols, and @what_to_export is an array telling what |
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216 | symbols *to* export (usually this is @_). The $package argument is |
217 | currently unused. |
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218 | |
219 | For example, suppose that you have a module, A, which already has an |
220 | import function: |
221 | |
222 | package A; |
223 | |
224 | @ISA = qw(Exporter); |
225 | @EXPORT_OK = qw ($b); |
226 | |
227 | sub import |
228 | { |
229 | $A::b = 1; # not a very useful import method |
230 | } |
231 | |
232 | and you want to Export symbol $A::b back to the module that called |
233 | package A. Since Exporter relies on the import method to work, via |
234 | inheritance, as it stands Exporter::import() will never get called. |
235 | Instead, say the following: |
236 | |
237 | package A; |
238 | @ISA = qw(Exporter); |
239 | @EXPORT_OK = qw ($b); |
240 | |
241 | sub import |
242 | { |
243 | $A::b = 1; |
244 | A->export_to_level(1, @_); |
245 | } |
246 | |
247 | This will export the symbols one level 'above' the current package - ie: to |
248 | the program or module that used package A. |
249 | |
250 | Note: Be careful not to modify '@_' at all before you call export_to_level |
251 | - or people using your package will get very unexplained results! |
252 | |
253 | |
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254 | =head2 Module Version Checking |
255 | |
256 | The Exporter module will convert an attempt to import a number from a |
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257 | module into a call to $module_name-E<gt>require_version($value). This can |
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258 | be used to validate that the version of the module being used is |
259 | greater than or equal to the required version. |
260 | |
261 | The Exporter module supplies a default require_version method which |
262 | checks the value of $VERSION in the exporting module. |
263 | |
264 | Since the default require_version method treats the $VERSION number as |
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265 | a simple numeric value it will regard version 1.10 as lower than |
266 | 1.9. For this reason it is strongly recommended that you use numbers |
267 | with at least two decimal places, e.g., 1.09. |
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268 | |
269 | =head2 Managing Unknown Symbols |
270 | |
271 | In some situations you may want to prevent certain symbols from being |
272 | exported. Typically this applies to extensions which have functions |
273 | or constants that may not exist on some systems. |
274 | |
275 | The names of any symbols that cannot be exported should be listed |
276 | in the C<@EXPORT_FAIL> array. |
277 | |
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278 | If a module attempts to import any of these symbols the Exporter |
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279 | will give the module an opportunity to handle the situation before |
280 | generating an error. The Exporter will call an export_fail method |
281 | with a list of the failed symbols: |
282 | |
283 | @failed_symbols = $module_name->export_fail(@failed_symbols); |
284 | |
285 | If the export_fail method returns an empty list then no error is |
286 | recorded and all the requested symbols are exported. If the returned |
287 | list is not empty then an error is generated for each symbol and the |
288 | export fails. The Exporter provides a default export_fail method which |
289 | simply returns the list unchanged. |
290 | |
291 | Uses for the export_fail method include giving better error messages |
292 | for some symbols and performing lazy architectural checks (put more |
293 | symbols into @EXPORT_FAIL by default and then take them out if someone |
294 | actually tries to use them and an expensive check shows that they are |
295 | usable on that platform). |
296 | |
297 | =head2 Tag Handling Utility Functions |
298 | |
299 | Since the symbols listed within %EXPORT_TAGS must also appear in either |
300 | @EXPORT or @EXPORT_OK, two utility functions are provided which allow |
301 | you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK: |
302 | |
303 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); |
304 | |
305 | Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT |
306 | Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK |
307 | |
308 | Any names which are not tags are added to @EXPORT or @EXPORT_OK |
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309 | unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags |
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310 | names being silently added to @EXPORT or @EXPORT_OK. Future versions |
311 | may make this a fatal error. |
312 | |
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313 | =head2 Generating combined tags |
314 | |
315 | If several symbol categories exist in %EXPORT_TAGS, it's usually |
316 | useful to create the utility ":all" to simplify "use" statements. |
317 | |
318 | The simplest way to do this is: |
319 | |
320 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); |
321 | |
322 | # add all the other ":class" tags to the ":all" class, |
323 | # deleting duplicates |
324 | { |
325 | my %seen; |
326 | |
327 | push @{$EXPORT_TAGS{all}}, |
328 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} foreach keys %EXPORT_TAGS; |
329 | } |
330 | |
331 | CGI.pm creates an ":all" tag which contains some (but not really |
332 | all) of its categories. That could be done with one small |
333 | change: |
334 | |
335 | # add some of the other ":class" tags to the ":all" class, |
336 | # deleting duplicates |
337 | { |
338 | my %seen; |
339 | |
340 | push @{$EXPORT_TAGS{all}}, |
341 | grep {!$seen{$_}++} @{$EXPORT_TAGS{$_}} |
342 | foreach qw/html2 html3 netscape form cgi internal/; |
343 | } |
344 | |
345 | Note that the tag names in %EXPORT_TAGS don't have the leading ':'. |
346 | |
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347 | =head2 C<AUTOLOAD>ed Constants |
348 | |
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349 | Many modules make use of C<AUTOLOAD>ing for constant subroutines to |
350 | avoid having to compile and waste memory on rarely used values (see |
351 | L<perlsub> for details on constant subroutines). Calls to such |
352 | constant subroutines are not optimized away at compile time because |
353 | they can't be checked at compile time for constancy. |
354 | |
355 | Even if a prototype is available at compile time, the body of the |
356 | subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to |
357 | examine both the C<()> prototype and the body of a subroutine at |
358 | compile time to detect that it can safely replace calls to that |
359 | subroutine with the constant value. |
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360 | |
361 | A workaround for this is to call the constants once in a C<BEGIN> block: |
362 | |
363 | package My ; |
364 | |
365 | use Socket ; |
366 | |
367 | foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime |
368 | BEGIN { SO_LINGER } |
369 | foo( SO_LINGER ); ## SO_LINGER optimized away at compile time. |
370 | |
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371 | This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before |
372 | SO_LINGER is encountered later in C<My> package. |
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373 | |
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374 | If you are writing a package that C<AUTOLOAD>s, consider forcing |
375 | an C<AUTOLOAD> for any constants explicitly imported by other packages |
376 | or which are usually used when your package is C<use>d. |
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377 | |
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378 | =cut |