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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "Encode::Encoding 3" | |
132 | .TH Encode::Encoding 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | Encode::Encoding \- Encode Implementation Base Class | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 2 | |
138 | \& package Encode::MyEncoding; | |
139 | \& use base qw(Encode::Encoding); | |
140 | .Ve | |
141 | .PP | |
142 | .Vb 1 | |
143 | \& __PACKAGE__->Define(qw(myCanonical myAlias)); | |
144 | .Ve | |
145 | .SH "DESCRIPTION" | |
146 | .IX Header "DESCRIPTION" | |
147 | As mentioned in Encode, encodings are (in the current | |
148 | implementation at least) defined as objects. The mapping of encoding | |
149 | name to object is via the \f(CW%Encode::Encoding\fR hash. Though you can | |
150 | directly manipulate this hash, it is strongly encouraged to use this | |
151 | base class module and add \fIencode()\fR and \fIdecode()\fR methods. | |
152 | .Sh "Methods you should implement" | |
153 | .IX Subsection "Methods you should implement" | |
154 | You are strongly encouraged to implement methods below, at least | |
155 | either \fIencode()\fR or \fIdecode()\fR. | |
156 | .IP "\->encode($string [,$check])" 4 | |
157 | .IX Item "->encode($string [,$check])" | |
158 | \&\s-1MUST\s0 return the octet sequence representing \fI$string\fR. | |
159 | .RS 4 | |
160 | .IP "*" 2 | |
161 | If \fI$check\fR is true, it \s-1SHOULD\s0 modify \fI$string\fR in place to remove | |
162 | the converted part (i.e. the whole string unless there is an error). | |
163 | If \fIperlio_ok()\fR is true, \s-1SHOULD\s0 becomes \s-1MUST\s0. | |
164 | .IP "*" 2 | |
165 | If an error occurs, it \s-1SHOULD\s0 return the octet sequence for the | |
166 | fragment of string that has been converted and modify \f(CW$string\fR in-place | |
167 | to remove the converted part leaving it starting with the problem | |
168 | fragment. If \fIperlio_ok()\fR is true, \s-1SHOULD\s0 becomes \s-1MUST\s0. | |
169 | .IP "*" 2 | |
170 | If \fI$check\fR is is false then \f(CW\*(C`encode\*(C'\fR \s-1MUST\s0 make a \*(L"best effort\*(R" to | |
171 | convert the string \- for example, by using a replacement character. | |
172 | .RE | |
173 | .RS 4 | |
174 | .RE | |
175 | .IP "\->decode($octets [,$check])" 4 | |
176 | .IX Item "->decode($octets [,$check])" | |
177 | \&\s-1MUST\s0 return the string that \fI$octets\fR represents. | |
178 | .RS 4 | |
179 | .IP "*" 2 | |
180 | If \fI$check\fR is true, it \s-1SHOULD\s0 modify \fI$octets\fR in place to remove | |
181 | the converted part (i.e. the whole sequence unless there is an | |
182 | error). If \fIperlio_ok()\fR is true, \s-1SHOULD\s0 becomes \s-1MUST\s0. | |
183 | .IP "*" 2 | |
184 | If an error occurs, it \s-1SHOULD\s0 return the fragment of string that has | |
185 | been converted and modify \f(CW$octets\fR in-place to remove the converted | |
186 | part leaving it starting with the problem fragment. If \fIperlio_ok()\fR is | |
187 | true, \s-1SHOULD\s0 becomes \s-1MUST\s0. | |
188 | .IP "*" 2 | |
189 | If \fI$check\fR is false then \f(CW\*(C`decode\*(C'\fR should make a \*(L"best effort\*(R" to | |
190 | convert the string \- for example by using Unicode's \*(L"\ex{\s-1FFFD\s0}\*(R" as a | |
191 | replacement character. | |
192 | .RE | |
193 | .RS 4 | |
194 | .RE | |
195 | .PP | |
196 | If you want your encoding to work with encoding pragma, you should | |
197 | also implement the method below. | |
198 | .ie n .IP "\->cat_decode($destination, $octets\fR, \f(CW$offset\fR, \f(CW$terminator [,$check])" 4 | |
199 | .el .IP "\->cat_decode($destination, \f(CW$octets\fR, \f(CW$offset\fR, \f(CW$terminator\fR [,$check])" 4 | |
200 | .IX Item "->cat_decode($destination, $octets, $offset, $terminator [,$check])" | |
201 | \&\s-1MUST\s0 decode \fI$octets\fR with \fI$offset\fR and concatenate it to \fI$destination\fR. | |
202 | Decoding will terminate when \f(CW$terminator\fR (a string) appears in output. | |
203 | \&\fI$offset\fR will be modified to the last \f(CW$octets\fR position at end of decode. | |
204 | Returns true if \f(CW$terminator\fR appears output, else returns false. | |
205 | .Sh "Other methods defined in Encode::Encodings" | |
206 | .IX Subsection "Other methods defined in Encode::Encodings" | |
207 | You do not have to override methods shown below unless you have to. | |
208 | .IP "\->name" 4 | |
209 | .IX Item "->name" | |
210 | Predefined As: | |
211 | .Sp | |
212 | .Vb 1 | |
213 | \& sub name { return shift->{'Name'} } | |
214 | .Ve | |
215 | .Sp | |
216 | \&\s-1MUST\s0 return the string representing the canonical name of the encoding. | |
217 | .IP "\->renew" 4 | |
218 | .IX Item "->renew" | |
219 | Predefined As: | |
220 | .Sp | |
221 | .Vb 6 | |
222 | \& sub renew { | |
223 | \& my $self = shift; | |
224 | \& my $clone = bless { %$self } => ref($self); | |
225 | \& $clone->{renewed}++; | |
226 | \& return $clone; | |
227 | \& } | |
228 | .Ve | |
229 | .Sp | |
230 | This method reconstructs the encoding object if necessary. If you need | |
231 | to store the state during encoding, this is where you clone your object. | |
232 | .Sp | |
233 | PerlIO \s-1ALWAYS\s0 calls this method to make sure it has its own private | |
234 | encoding object. | |
235 | .IP "\->renewed" 4 | |
236 | .IX Item "->renewed" | |
237 | Predefined As: | |
238 | .Sp | |
239 | .Vb 1 | |
240 | \& sub renewed { $_[0]->{renewed} || 0 } | |
241 | .Ve | |
242 | .Sp | |
243 | Tells whether the object is renewed (and how many times). Some | |
244 | modules emit \f(CW\*(C`Use of uninitialized value in null operation\*(C'\fR warning | |
245 | unless the value is numeric so return 0 for false. | |
246 | .IP "\->\fIperlio_ok()\fR" 4 | |
247 | .IX Item "->perlio_ok()" | |
248 | Predefined As: | |
249 | .Sp | |
250 | .Vb 4 | |
251 | \& sub perlio_ok { | |
252 | \& eval{ require PerlIO::encoding }; | |
253 | \& return $@ ? 0 : 1; | |
254 | \& } | |
255 | .Ve | |
256 | .Sp | |
257 | If your encoding does not support PerlIO for some reasons, just; | |
258 | .Sp | |
259 | .Vb 1 | |
260 | \& sub perlio_ok { 0 } | |
261 | .Ve | |
262 | .IP "\->\fIneeds_lines()\fR" 4 | |
263 | .IX Item "->needs_lines()" | |
264 | Predefined As: | |
265 | .Sp | |
266 | .Vb 1 | |
267 | \& sub needs_lines { 0 }; | |
268 | .Ve | |
269 | .Sp | |
270 | If your encoding can work with PerlIO but needs line buffering, you | |
271 | \&\s-1MUST\s0 define this method so it returns true. 7bit \s-1ISO\-2022\s0 encodings | |
272 | are one example that needs this. When this method is missing, false | |
273 | is assumed. | |
274 | .Sh "Example: Encode::ROT13" | |
275 | .IX Subsection "Example: Encode::ROT13" | |
276 | .Vb 3 | |
277 | \& package Encode::ROT13; | |
278 | \& use strict; | |
279 | \& use base qw(Encode::Encoding); | |
280 | .Ve | |
281 | .PP | |
282 | .Vb 1 | |
283 | \& __PACKAGE__->Define('rot13'); | |
284 | .Ve | |
285 | .PP | |
286 | .Vb 6 | |
287 | \& sub encode($$;$){ | |
288 | \& my ($obj, $str, $chk) = @_; | |
289 | \& $str =~ tr/A-Za-z/N-ZA-Mn-za-m/; | |
290 | \& $_[1] = '' if $chk; # this is what in-place edit means | |
291 | \& return $str; | |
292 | \& } | |
293 | .Ve | |
294 | .PP | |
295 | .Vb 2 | |
296 | \& # Jr pna or ynml yvxr guvf; | |
297 | \& *decode = \e&encode; | |
298 | .Ve | |
299 | .PP | |
300 | .Vb 1 | |
301 | \& 1; | |
302 | .Ve | |
303 | .SH "Why the heck Encode API is different?" | |
304 | .IX Header "Why the heck Encode API is different?" | |
305 | It should be noted that the \fI$check\fR behaviour is different from the | |
306 | outer public \s-1API\s0. The logic is that the \*(L"unchecked\*(R" case is useful | |
307 | when the encoding is part of a stream which may be reporting errors | |
308 | (e.g. \s-1STDERR\s0). In such cases, it is desirable to get everything | |
309 | through somehow without causing additional errors which obscure the | |
310 | original one. Also, the encoding is best placed to know what the | |
311 | correct replacement character is, so if that is the desired behaviour | |
312 | then letting low level code do it is the most efficient. | |
313 | .PP | |
314 | By contrast, if \fI$check\fR is true, the scheme above allows the | |
315 | encoding to do as much as it can and tell the layer above how much | |
316 | that was. What is lacking at present is a mechanism to report what | |
317 | went wrong. The most likely interface will be an additional method | |
318 | call to the object, or perhaps (to avoid forcing per-stream objects | |
319 | on otherwise stateless encodings) an additional parameter. | |
320 | .PP | |
321 | It is also highly desirable that encoding classes inherit from | |
322 | \&\f(CW\*(C`Encode::Encoding\*(C'\fR as a base class. This allows that class to define | |
323 | additional behaviour for all encoding objects. | |
324 | .PP | |
325 | .Vb 2 | |
326 | \& package Encode::MyEncoding; | |
327 | \& use base qw(Encode::Encoding); | |
328 | .Ve | |
329 | .PP | |
330 | .Vb 1 | |
331 | \& __PACKAGE__->Define(qw(myCanonical myAlias)); | |
332 | .Ve | |
333 | .PP | |
334 | to create an object with \f(CW\*(C`bless {Name => ...}, $class\*(C'\fR, and call | |
335 | define_encoding. They inherit their \f(CW\*(C`name\*(C'\fR method from | |
336 | \&\f(CW\*(C`Encode::Encoding\*(C'\fR. | |
337 | .Sh "Compiled Encodings" | |
338 | .IX Subsection "Compiled Encodings" | |
339 | For the sake of speed and efficiency, most of the encodings are now | |
340 | supported via a \fIcompiled form\fR: \s-1XS\s0 modules generated from \s-1UCM\s0 | |
341 | files. Encode provides the enc2xs tool to achieve that. Please see | |
342 | enc2xs for more details. | |
343 | .SH "SEE ALSO" | |
344 | .IX Header "SEE ALSO" | |
345 | perlmod, enc2xs |