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1 | package Exporter; |
2 | |
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3 | require 5.001; |
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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 = '5.564'; |
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 | |
38 | my($exports, $export_cache) = (\@{"$pkg\::EXPORT"}, |
39 | \%{"$pkg\::EXPORT"}); |
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40 | # We *need* to treat @{"$pkg\::EXPORT_FAIL"} since Carp uses it :-( |
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41 | my($fail) = \@{"$pkg\::EXPORT_FAIL"}; |
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42 | return export $pkg, $callpkg, @_ |
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43 | if $Verbose or $Debug or @$fail > 1; |
44 | my $args = @_ or @_ = @$exports; |
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45 | |
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46 | if ($args and not %$export_cache) { |
47 | foreach my $sym (@$exports, @{"$pkg\::EXPORT_OK"}) { |
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48 | $sym =~ s/^&//; |
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49 | $export_cache->{$sym} = 1; |
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50 | } |
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51 | } |
52 | if ($Verbose or $Debug |
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53 | or grep {/\W/ or $args and not exists $export_cache->{$_} |
54 | or @$fail and $_ eq $fail->[0] |
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55 | or (@{"$pkg\::EXPORT_OK"} |
56 | and $_ eq ${"$pkg\::EXPORT_OK"}[0])} @_) { |
57 | return export $pkg, $callpkg, ($args ? @_ : ()); |
58 | } |
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59 | local $SIG{__WARN__} = |
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60 | sub {require Carp; &Carp::carp}; |
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61 | foreach my $sym (@_) { |
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62 | # shortcut for the common case of no type character |
63 | *{"$callpkg\::$sym"} = \&{"$pkg\::$sym"}; |
64 | } |
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65 | } |
66 | |
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67 | |
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68 | # Default methods |
69 | |
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70 | sub export_fail { |
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71 | my $self = shift; |
72 | @_; |
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73 | } |
74 | |
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75 | |
76 | sub require_version { |
77 | require Exporter::Heavy; |
78 | goto &Exporter::Heavy::require_version; |
79 | } |
80 | |
81 | |
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82 | 1; |
83 | |
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84 | |
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85 | =head1 NAME |
86 | |
87 | Exporter - Implements default import method for modules |
88 | |
89 | =head1 SYNOPSIS |
90 | |
91 | In module ModuleName.pm: |
92 | |
93 | package ModuleName; |
94 | require Exporter; |
95 | @ISA = qw(Exporter); |
96 | |
97 | @EXPORT = qw(...); # symbols to export by default |
98 | @EXPORT_OK = qw(...); # symbols to export on request |
99 | %EXPORT_TAGS = tag => [...]; # define names for sets of symbols |
100 | |
101 | In other files which wish to use ModuleName: |
102 | |
103 | use ModuleName; # import default symbols into my package |
104 | |
105 | use ModuleName qw(...); # import listed symbols into my package |
106 | |
107 | use ModuleName (); # do not import any symbols |
108 | |
109 | =head1 DESCRIPTION |
110 | |
111 | The Exporter module implements a default C<import> method which |
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112 | many modules choose to inherit rather than implement their own. |
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113 | |
114 | Perl automatically calls the C<import> method when processing a |
115 | C<use> statement for a module. Modules and C<use> are documented |
116 | in L<perlfunc> and L<perlmod>. Understanding the concept of |
117 | modules and how the C<use> statement operates is important to |
118 | understanding the Exporter. |
119 | |
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120 | =head2 How to Export |
121 | |
122 | The arrays C<@EXPORT> and C<@EXPORT_OK> in a module hold lists of |
123 | symbols that are going to be exported into the users name space by |
124 | default, or which they can request to be exported, respectively. The |
125 | symbols can represent functions, scalars, arrays, hashes, or typeglobs. |
126 | The symbols must be given by full name with the exception that the |
127 | ampersand in front of a function is optional, e.g. |
128 | |
129 | @EXPORT = qw(afunc $scalar @array); # afunc is a function |
130 | @EXPORT_OK = qw(&bfunc %hash *typeglob); # explicit prefix on &bfunc |
131 | |
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132 | =head2 Selecting What To Export |
133 | |
134 | Do B<not> export method names! |
135 | |
136 | Do B<not> export anything else by default without a good reason! |
137 | |
138 | Exports pollute the namespace of the module user. If you must export |
139 | try to use @EXPORT_OK in preference to @EXPORT and avoid short or |
140 | common symbol names to reduce the risk of name clashes. |
141 | |
142 | Generally anything not exported is still accessible from outside the |
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143 | module using the ModuleName::item_name (or $blessed_ref-E<gt>method) |
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144 | syntax. By convention you can use a leading underscore on names to |
145 | informally indicate that they are 'internal' and not for public use. |
146 | |
147 | (It is actually possible to get private functions by saying: |
148 | |
149 | my $subref = sub { ... }; |
150 | &$subref; |
151 | |
152 | But there's no way to call that directly as a method, since a method |
153 | must have a name in the symbol table.) |
154 | |
155 | As a general rule, if the module is trying to be object oriented |
156 | then export nothing. If it's just a collection of functions then |
157 | @EXPORT_OK anything but use @EXPORT with caution. |
158 | |
159 | Other module design guidelines can be found in L<perlmod>. |
160 | |
161 | =head2 Specialised Import Lists |
162 | |
163 | If the first entry in an import list begins with !, : or / then the |
164 | list is treated as a series of specifications which either add to or |
165 | delete from the list of names to import. They are processed left to |
166 | right. Specifications are in the form: |
167 | |
168 | [!]name This name only |
169 | [!]:DEFAULT All names in @EXPORT |
170 | [!]:tag All names in $EXPORT_TAGS{tag} anonymous list |
171 | [!]/pattern/ All names in @EXPORT and @EXPORT_OK which match |
172 | |
173 | A leading ! indicates that matching names should be deleted from the |
174 | list of names to import. If the first specification is a deletion it |
175 | is treated as though preceded by :DEFAULT. If you just want to import |
176 | extra names in addition to the default set you will still need to |
177 | include :DEFAULT explicitly. |
178 | |
179 | e.g., Module.pm defines: |
180 | |
181 | @EXPORT = qw(A1 A2 A3 A4 A5); |
182 | @EXPORT_OK = qw(B1 B2 B3 B4 B5); |
183 | %EXPORT_TAGS = (T1 => [qw(A1 A2 B1 B2)], T2 => [qw(A1 A2 B3 B4)]); |
184 | |
185 | Note that you cannot use tags in @EXPORT or @EXPORT_OK. |
186 | Names in EXPORT_TAGS must also appear in @EXPORT or @EXPORT_OK. |
187 | |
188 | An application using Module can say something like: |
189 | |
190 | use Module qw(:DEFAULT :T2 !B3 A3); |
191 | |
192 | Other examples include: |
193 | |
194 | use Socket qw(!/^[AP]F_/ !SOMAXCONN !SOL_SOCKET); |
195 | use POSIX qw(:errno_h :termios_h !TCSADRAIN !/^EXIT/); |
196 | |
197 | Remember that most patterns (using //) will need to be anchored |
198 | with a leading ^, e.g., C</^EXIT/> rather than C</EXIT/>. |
199 | |
200 | You can say C<BEGIN { $Exporter::Verbose=1 }> to see how the |
201 | specifications are being processed and what is actually being imported |
202 | into modules. |
203 | |
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204 | =head2 Exporting without using Export's import method |
205 | |
206 | Exporter has a special method, 'export_to_level' which is used in situations |
207 | where you can't directly call Export's import method. The export_to_level |
208 | method looks like: |
209 | |
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210 | MyPackage->export_to_level($where_to_export, $package, @what_to_export); |
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211 | |
212 | where $where_to_export is an integer telling how far up the calling stack |
213 | to export your symbols, and @what_to_export is an array telling what |
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214 | symbols *to* export (usually this is @_). The $package argument is |
215 | currently unused. |
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216 | |
217 | For example, suppose that you have a module, A, which already has an |
218 | import function: |
219 | |
220 | package A; |
221 | |
222 | @ISA = qw(Exporter); |
223 | @EXPORT_OK = qw ($b); |
224 | |
225 | sub import |
226 | { |
227 | $A::b = 1; # not a very useful import method |
228 | } |
229 | |
230 | and you want to Export symbol $A::b back to the module that called |
231 | package A. Since Exporter relies on the import method to work, via |
232 | inheritance, as it stands Exporter::import() will never get called. |
233 | Instead, say the following: |
234 | |
235 | package A; |
236 | @ISA = qw(Exporter); |
237 | @EXPORT_OK = qw ($b); |
238 | |
239 | sub import |
240 | { |
241 | $A::b = 1; |
242 | A->export_to_level(1, @_); |
243 | } |
244 | |
245 | This will export the symbols one level 'above' the current package - ie: to |
246 | the program or module that used package A. |
247 | |
248 | Note: Be careful not to modify '@_' at all before you call export_to_level |
249 | - or people using your package will get very unexplained results! |
250 | |
251 | |
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252 | =head2 Module Version Checking |
253 | |
254 | The Exporter module will convert an attempt to import a number from a |
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255 | module into a call to $module_name-E<gt>require_version($value). This can |
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256 | be used to validate that the version of the module being used is |
257 | greater than or equal to the required version. |
258 | |
259 | The Exporter module supplies a default require_version method which |
260 | checks the value of $VERSION in the exporting module. |
261 | |
262 | Since the default require_version method treats the $VERSION number as |
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263 | a simple numeric value it will regard version 1.10 as lower than |
264 | 1.9. For this reason it is strongly recommended that you use numbers |
265 | with at least two decimal places, e.g., 1.09. |
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266 | |
267 | =head2 Managing Unknown Symbols |
268 | |
269 | In some situations you may want to prevent certain symbols from being |
270 | exported. Typically this applies to extensions which have functions |
271 | or constants that may not exist on some systems. |
272 | |
273 | The names of any symbols that cannot be exported should be listed |
274 | in the C<@EXPORT_FAIL> array. |
275 | |
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276 | If a module attempts to import any of these symbols the Exporter |
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277 | will give the module an opportunity to handle the situation before |
278 | generating an error. The Exporter will call an export_fail method |
279 | with a list of the failed symbols: |
280 | |
281 | @failed_symbols = $module_name->export_fail(@failed_symbols); |
282 | |
283 | If the export_fail method returns an empty list then no error is |
284 | recorded and all the requested symbols are exported. If the returned |
285 | list is not empty then an error is generated for each symbol and the |
286 | export fails. The Exporter provides a default export_fail method which |
287 | simply returns the list unchanged. |
288 | |
289 | Uses for the export_fail method include giving better error messages |
290 | for some symbols and performing lazy architectural checks (put more |
291 | symbols into @EXPORT_FAIL by default and then take them out if someone |
292 | actually tries to use them and an expensive check shows that they are |
293 | usable on that platform). |
294 | |
295 | =head2 Tag Handling Utility Functions |
296 | |
297 | Since the symbols listed within %EXPORT_TAGS must also appear in either |
298 | @EXPORT or @EXPORT_OK, two utility functions are provided which allow |
299 | you to easily add tagged sets of symbols to @EXPORT or @EXPORT_OK: |
300 | |
301 | %EXPORT_TAGS = (foo => [qw(aa bb cc)], bar => [qw(aa cc dd)]); |
302 | |
303 | Exporter::export_tags('foo'); # add aa, bb and cc to @EXPORT |
304 | Exporter::export_ok_tags('bar'); # add aa, cc and dd to @EXPORT_OK |
305 | |
306 | Any names which are not tags are added to @EXPORT or @EXPORT_OK |
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307 | unchanged but will trigger a warning (with C<-w>) to avoid misspelt tags |
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308 | names being silently added to @EXPORT or @EXPORT_OK. Future versions |
309 | may make this a fatal error. |
310 | |
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311 | =head2 C<AUTOLOAD>ed Constants |
312 | |
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313 | Many modules make use of C<AUTOLOAD>ing for constant subroutines to |
314 | avoid having to compile and waste memory on rarely used values (see |
315 | L<perlsub> for details on constant subroutines). Calls to such |
316 | constant subroutines are not optimized away at compile time because |
317 | they can't be checked at compile time for constancy. |
318 | |
319 | Even if a prototype is available at compile time, the body of the |
320 | subroutine is not (it hasn't been C<AUTOLOAD>ed yet). perl needs to |
321 | examine both the C<()> prototype and the body of a subroutine at |
322 | compile time to detect that it can safely replace calls to that |
323 | subroutine with the constant value. |
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324 | |
325 | A workaround for this is to call the constants once in a C<BEGIN> block: |
326 | |
327 | package My ; |
328 | |
329 | use Socket ; |
330 | |
331 | foo( SO_LINGER ); ## SO_LINGER NOT optimized away; called at runtime |
332 | BEGIN { SO_LINGER } |
333 | foo( SO_LINGER ); ## SO_LINGER optimized away at compile time. |
334 | |
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335 | This forces the C<AUTOLOAD> for C<SO_LINGER> to take place before |
336 | SO_LINGER is encountered later in C<My> package. |
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337 | |
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338 | If you are writing a package that C<AUTOLOAD>s, consider forcing |
339 | an C<AUTOLOAD> for any constants explicitly imported by other packages |
340 | or which are usually used when your package is C<use>d. |
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341 | |
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342 | =cut |