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1 | =head1 NAME |
2 | |
3 | perlreapi - perl regular expression plugin interface |
4 | |
5 | =head1 DESCRIPTION |
6 | |
7 | As of Perl 5.9.5 there is a new interface for using other regexp engines than |
8 | the default one. Each engine is supposed to provide access to a constant |
9 | structure of the following format: |
10 | |
11 | typedef struct regexp_engine { |
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12 | REGEXP* (*comp) (pTHX_ const SV * const pattern, const U32 flags); |
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13 | I32 (*exec) (pTHX_ REGEXP * const rx, char* stringarg, char* strend, |
14 | char* strbeg, I32 minend, SV* screamer, |
15 | void* data, U32 flags); |
16 | char* (*intuit) (pTHX_ REGEXP * const rx, SV *sv, char *strpos, |
17 | char *strend, U32 flags, |
18 | struct re_scream_pos_data_s *data); |
19 | SV* (*checkstr) (pTHX_ REGEXP * const rx); |
20 | void (*free) (pTHX_ REGEXP * const rx); |
21 | void (*numbered_buff_get) (pTHX_ REGEXP * const rx, |
22 | const I32 paren, SV * const usesv); |
23 | SV* (*named_buff_get)(pTHX_ REGEXP * const rx, SV * const namesv, |
24 | const U32 flags); |
25 | SV* (*qr_package)(pTHX_ REGEXP * const rx); |
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26 | #ifdef USE_ITHREADS |
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27 | void* (*dupe) (pTHX_ REGEXP * const rx, CLONE_PARAMS *param); |
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28 | #endif |
29 | } regexp_engine; |
30 | |
31 | When a regexp is compiled, its C<engine> field is then set to point at |
32 | the appropriate structure so that when it needs to be used Perl can find |
33 | the right routines to do so. |
34 | |
35 | In order to install a new regexp handler, C<$^H{regcomp}> is set |
36 | to an integer which (when casted appropriately) resolves to one of these |
37 | structures. When compiling, the C<comp> method is executed, and the |
38 | resulting regexp structure's engine field is expected to point back at |
39 | the same structure. |
40 | |
41 | The pTHX_ symbol in the definition is a macro used by perl under threading |
42 | to provide an extra argument to the routine holding a pointer back to |
43 | the interpreter that is executing the regexp. So under threading all |
44 | routines get an extra argument. |
45 | |
46 | The routines are as follows: |
47 | |
48 | =head2 comp |
49 | |
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50 | REGEXP* comp(pTHX_ const SV * const pattern, const U32 flags); |
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51 | |
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52 | Compile the pattern stored in C<pattern> using the given C<flags> and |
53 | return a pointer to a prepared C<REGEXP> structure that can perform |
54 | the match. See L</The REGEXP structure> below for an explanation of |
55 | the individual fields in the REGEXP struct. |
56 | |
57 | The C<pattern> parameter is the scalar that was used as the |
58 | pattern. previous versions of perl would pass two C<char*> indicating |
59 | the start and end of the stringifed pattern, the following snippet can |
60 | be used to get the old parameters: |
61 | |
62 | STRLEN plen; |
63 | char* exp = SvPV(pattern, plen); |
64 | char* xend = exp + plen; |
65 | |
66 | Since any scalar can be passed as a pattern it's possible to implement |
67 | an engine that does something with an array (C<< "ook" =~ [ qw/ eek |
68 | hlagh / ] >>) or with the non-stringified form of a compiled regular |
69 | expression (C<< "ook" =~ qr/eek/ >>). perl's own engine will always |
70 | stringify everything using the snippet above but that doesn't mean |
71 | other engines have to. |
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72 | |
73 | The C<flags> paramater is a bitfield which indicates which of the |
74 | C<msixk> flags the regex was compiled with. In addition it contains |
75 | info about whether C<use locale> is in effect and optimization info |
76 | for C<split>. A regex engine might want to use the same split |
77 | optimizations with a different syntax, for instance a Perl6 engine |
78 | would treat C<split /^^/> equivalently to perl's C<split /^/>, see |
79 | L<split documentation|perlfunc> and the relevant code in C<pp_split> |
80 | in F<pp.c> to find out whether your engine should be setting these. |
81 | |
82 | The C<eogc> flags are stripped out before being passed to the comp |
83 | routine. The regex engine does not need to know whether any of these |
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84 | are set as those flags should only affect what perl does with the |
85 | pattern and its match variables, not how it gets compiled & executed. |
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86 | |
87 | =over 4 |
88 | |
89 | =item RXf_SKIPWHITE |
90 | |
91 | C<split ' '> or C<split> with no arguments (which really means |
92 | C<split(' ', $_> see L<split|perlfunc>). |
93 | |
94 | =item RXf_START_ONLY |
95 | |
96 | Set if the pattern is C</^/> (C<<r->prelen == 1 && r->precomp[0] == |
97 | '^'>>). Will be used by the C<split> operator to split the given |
98 | string on C<\n> (even under C</^/s>, see L<split|perlfunc>). |
99 | |
100 | =item RXf_WHITE |
101 | |
102 | Set if the pattern is exactly C</\s+/> and used by C<split>, the |
103 | definition of whitespace varies depending on whether RXf_UTF8 or |
104 | RXf_PMf_LOCALE is set. |
105 | |
106 | =item RXf_PMf_LOCALE |
107 | |
108 | Makes C<split> use the locale dependant definition of whitespace under C<use |
109 | locale> when RXf_SKIPWHITE or RXf_WHITE is in effect. Under ASCII whitespace is |
110 | defined as per L<isSPACE|perlapi/ISSPACE>, and by the internal macros |
111 | C<is_utf8_space> under UTF-8 and C<isSPACE_LC> under C<use locale>. |
112 | |
113 | =item RXf_PMf_MULTILINE |
114 | |
115 | The C</m> flag, this ends up being passed to C<Perl_fbm_instr> by |
116 | C<pp_split> regardless of the engine. |
117 | |
118 | =item RXf_PMf_SINGLELINE |
119 | |
120 | The C</s> flag. Guaranteed not to be used outside the regex engine. |
121 | |
122 | =item RXf_PMf_FOLD |
123 | |
124 | The C</i> flag. Guaranteed not to be used outside the regex engine. |
125 | |
126 | =item RXf_PMf_EXTENDED |
127 | |
128 | The C</x> flag. Guaranteed not to be used outside the regex |
129 | engine. However if present on a regex C<#> comments will be stripped |
130 | by the tokenizer regardless of the engine currently in use. |
131 | |
132 | =item RXf_PMf_KEEPCOPY |
133 | |
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134 | The C</p> flag. |
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135 | |
136 | =item RXf_UTF8 |
137 | |
138 | Set if the pattern is L<SvUTF8()|perlapi/SvUTF8>, set by Perl_pmruntime. |
139 | |
140 | =back |
141 | |
142 | In general these flags should be preserved in regex->extflags after |
143 | compilation, although it is possible the regex includes constructs |
144 | that changes them. The perl engine for instance may upgrade non-utf8 |
145 | strings to utf8 if the pattern includes constructs such as C<\x{...}> |
146 | that can only match unicode values. RXf_SKIPWHITE should always be |
147 | preserved verbatim in regex->extflags. |
148 | |
149 | =head2 exec |
150 | |
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151 | I32 exec(pTHX_ REGEXP * const rx, |
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152 | char *stringarg, char* strend, char* strbeg, |
153 | I32 minend, SV* screamer, |
154 | void* data, U32 flags); |
155 | |
156 | Execute a regexp. |
157 | |
158 | =head2 intuit |
159 | |
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160 | char* intuit(pTHX_ REGEXP * const rx, |
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161 | SV *sv, char *strpos, char *strend, |
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162 | const U32 flags, struct re_scream_pos_data_s *data); |
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163 | |
164 | Find the start position where a regex match should be attempted, |
165 | or possibly whether the regex engine should not be run because the |
166 | pattern can't match. This is called as appropriate by the core |
167 | depending on the values of the extflags member of the regexp |
168 | structure. |
169 | |
170 | =head2 checkstr |
171 | |
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172 | SV* checkstr(pTHX_ REGEXP * const rx); |
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173 | |
174 | Return a SV containing a string that must appear in the pattern. Used |
175 | by C<split> for optimising matches. |
176 | |
177 | =head2 free |
178 | |
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179 | void free(pTHX_ REGEXP * const rx); |
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180 | |
181 | Called by perl when it is freeing a regexp pattern so that the engine |
182 | can release any resources pointed to by the C<pprivate> member of the |
183 | regexp structure. This is only responsible for freeing private data; |
184 | perl will handle releasing anything else contained in the regexp structure. |
185 | |
186 | =head2 numbered_buff_get |
187 | |
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188 | void numbered_buff_get(pTHX_ REGEXP * const rx, const I32 paren, |
189 | SV * const usesv); |
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190 | |
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191 | Called to get the value of C<$`>, C<$'>, C<$&> (and their named |
192 | equivalents, see L<perlvar>) and the numbered capture buffers (C<$1>, |
193 | C<$2>, ...). |
194 | |
195 | The C<paren> paramater will be C<-2> for C<$`>, C<-1> for C<$'>, C<0> |
196 | for C<$&>, C<1> for C<$1> and so forth. |
197 | |
198 | C<usesv> should be set to the scalar to return, the scalar is passed |
199 | as an argument rather than being returned from the function because |
200 | when it's called perl already has a scalar to store the value, |
201 | creating another one would be redundant. The scalar can be set with |
202 | C<sv_setsv>, C<sv_setpvn> and friends, see L<perlapi>. |
203 | |
204 | This callback is where perl untaints its own capture variables under |
205 | taint mode (see L<perlsec>). See the C<Perl_reg_numbered_buff_get> |
206 | function in F<regcomp.c> for how to untaint capture variables if |
207 | that's something you'd like your engine to do as well. |
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208 | |
209 | =head2 named_buff_get |
210 | |
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211 | SV* named_buff_get(pTHX_ REGEXP * const rx, SV * const namesv, |
212 | const U32 flags); |
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213 | |
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214 | Called to get the value of key in the C<%+> and C<%-> hashes, |
215 | C<namesv> is the hash key being requested and if C<flags & 1> is true |
216 | C<%-> is being requested (and C<%+> if it's not). |
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217 | |
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218 | =head2 qr_package |
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219 | |
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220 | SV* qr_package(pTHX_ REGEXP * const rx); |
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221 | |
222 | The package the qr// magic object is blessed into (as seen by C<ref |
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223 | qr//>). It is recommended that engines change this to their package |
224 | name for identification regardless of whether they implement methods |
225 | on the object. |
226 | |
227 | A callback implementation might be: |
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228 | |
229 | SV* |
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230 | Example_reg_qr_package(pTHX_ REGEXP * const rx) |
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231 | { |
232 | PERL_UNUSED_ARG(rx); |
233 | return newSVpvs("re::engine::Example"); |
234 | } |
235 | |
236 | Any method calls on an object created with C<qr//> will be dispatched to the |
237 | package as a normal object. |
238 | |
239 | use re::engine::Example; |
240 | my $re = qr//; |
241 | $re->meth; # dispatched to re::engine::Example::meth() |
242 | |
243 | To retrieve the C<REGEXP> object from the scalar in an XS function use the |
244 | following snippet: |
245 | |
246 | void meth(SV * rv) |
247 | PPCODE: |
248 | MAGIC * mg; |
249 | REGEXP * re; |
250 | |
251 | if (SvMAGICAL(sv)) |
252 | mg_get(sv); |
253 | if (SvROK(sv) && |
254 | (sv = (SV*)SvRV(sv)) && /* assignment deliberate */ |
255 | SvTYPE(sv) == SVt_PVMG && |
256 | (mg = mg_find(sv, PERL_MAGIC_qr))) /* assignment deliberate */ |
257 | { |
258 | re = (REGEXP *)mg->mg_obj; |
259 | } |
260 | |
261 | Or use the (CURRENTLY UNDOCUMENETED!) C<Perl_get_re_arg> function: |
262 | |
263 | void meth(SV * rv) |
264 | PPCODE: |
265 | const REGEXP * const re = (REGEXP *)Perl_get_re_arg( aTHX_ rv, 0, NULL ); |
266 | |
267 | =head2 dupe |
268 | |
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269 | void* dupe(pTHX_ REGEXP * const rx, CLONE_PARAMS *param); |
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270 | |
271 | On threaded builds a regexp may need to be duplicated so that the pattern |
272 | can be used by mutiple threads. This routine is expected to handle the |
273 | duplication of any private data pointed to by the C<pprivate> member of |
274 | the regexp structure. It will be called with the preconstructed new |
275 | regexp structure as an argument, the C<pprivate> member will point at |
276 | the B<old> private structue, and it is this routine's responsibility to |
277 | construct a copy and return a pointer to it (which perl will then use to |
278 | overwrite the field as passed to this routine.) |
279 | |
280 | This allows the engine to dupe its private data but also if necessary |
281 | modify the final structure if it really must. |
282 | |
283 | On unthreaded builds this field doesn't exist. |
284 | |
285 | =head1 The REGEXP structure |
286 | |
287 | The REGEXP struct is defined in F<regexp.h>. All regex engines must be able to |
288 | correctly build such a structure in their L</comp> routine. |
289 | |
290 | The REGEXP structure contains all the data that perl needs to be aware of |
291 | to properly work with the regular expression. It includes data about |
292 | optimisations that perl can use to determine if the regex engine should |
293 | really be used, and various other control info that is needed to properly |
294 | execute patterns in various contexts such as is the pattern anchored in |
295 | some way, or what flags were used during the compile, or whether the |
296 | program contains special constructs that perl needs to be aware of. |
297 | |
298 | In addition it contains two fields that are intended for the private use |
299 | of the regex engine that compiled the pattern. These are the C<intflags> |
300 | and pprivate members. The C<pprivate> is a void pointer to an arbitrary |
301 | structure whose use and management is the responsibility of the compiling |
302 | engine. perl will never modify either of these values. |
303 | |
304 | typedef struct regexp { |
305 | /* what engine created this regexp? */ |
306 | const struct regexp_engine* engine; |
307 | |
308 | /* what re is this a lightweight copy of? */ |
309 | struct regexp* mother_re; |
310 | |
311 | /* Information about the match that the perl core uses to manage things */ |
312 | U32 extflags; /* Flags used both externally and internally */ |
313 | I32 minlen; /* mininum possible length of string to match */ |
314 | I32 minlenret; /* mininum possible length of $& */ |
315 | U32 gofs; /* chars left of pos that we search from */ |
316 | |
317 | /* substring data about strings that must appear |
318 | in the final match, used for optimisations */ |
319 | struct reg_substr_data *substrs; |
320 | |
321 | U32 nparens; /* number of capture buffers */ |
322 | |
323 | /* private engine specific data */ |
324 | U32 intflags; /* Engine Specific Internal flags */ |
325 | void *pprivate; /* Data private to the regex engine which |
326 | created this object. */ |
327 | |
328 | /* Data about the last/current match. These are modified during matching*/ |
329 | U32 lastparen; /* last open paren matched */ |
330 | U32 lastcloseparen; /* last close paren matched */ |
331 | regexp_paren_pair *swap; /* Swap copy of *offs */ |
332 | regexp_paren_pair *offs; /* Array of offsets for (@-) and (@+) */ |
333 | |
334 | char *subbeg; /* saved or original string so \digit works forever. */ |
335 | SV_SAVED_COPY /* If non-NULL, SV which is COW from original */ |
336 | I32 sublen; /* Length of string pointed by subbeg */ |
337 | |
338 | /* Information about the match that isn't often used */ |
339 | I32 prelen; /* length of precomp */ |
340 | const char *precomp; /* pre-compilation regular expression */ |
341 | |
342 | /* wrapped can't be const char*, as it is returned by sv_2pv_flags */ |
343 | char *wrapped; /* wrapped version of the pattern */ |
344 | I32 wraplen; /* length of wrapped */ |
345 | |
346 | I32 seen_evals; /* number of eval groups in the pattern - for security checks */ |
347 | HV *paren_names; /* Optional hash of paren names */ |
348 | |
349 | /* Refcount of this regexp */ |
350 | I32 refcnt; /* Refcount of this regexp */ |
351 | } regexp; |
352 | |
353 | The fields are discussed in more detail below: |
354 | |
355 | =over 4 |
356 | |
357 | =item C<engine> |
358 | |
359 | This field points at a regexp_engine structure which contains pointers |
360 | to the subroutines that are to be used for performing a match. It |
361 | is the compiling routine's responsibility to populate this field before |
362 | returning the regexp object. |
363 | |
364 | Internally this is set to C<NULL> unless a custom engine is specified in |
365 | C<$^H{regcomp}>, perl's own set of callbacks can be accessed in the struct |
366 | pointed to by C<RE_ENGINE_PTR>. |
367 | |
368 | =item C<mother_re> |
369 | |
370 | TODO, see L<http://www.mail-archive.com/perl5-changes@perl.org/msg17328.html> |
371 | |
372 | =item C<extflags> |
373 | |
374 | This will be used by perl to see what flags the regexp was compiled with, this |
375 | will normally be set to the value of the flags parameter on L</comp>. |
376 | |
377 | =item C<minlen> C<minlenret> |
378 | |
379 | The minimum string length required for the pattern to match. This is used to |
380 | prune the search space by not bothering to match any closer to the end of a |
381 | string than would allow a match. For instance there is no point in even |
382 | starting the regex engine if the minlen is 10 but the string is only 5 |
383 | characters long. There is no way that the pattern can match. |
384 | |
385 | C<minlenret> is the minimum length of the string that would be found |
386 | in $& after a match. |
387 | |
388 | The difference between C<minlen> and C<minlenret> can be seen in the |
389 | following pattern: |
390 | |
391 | /ns(?=\d)/ |
392 | |
393 | where the C<minlen> would be 3 but C<minlenret> would only be 2 as the \d is |
394 | required to match but is not actually included in the matched content. This |
395 | distinction is particularly important as the substitution logic uses the |
396 | C<minlenret> to tell whether it can do in-place substition which can result in |
397 | considerable speedup. |
398 | |
399 | =item C<gofs> |
400 | |
401 | Left offset from pos() to start match at. |
402 | |
403 | =item C<substrs> |
404 | |
405 | TODO: document |
406 | |
407 | =item C<nparens>, C<lasparen>, and C<lastcloseparen> |
408 | |
409 | These fields are used to keep track of how many paren groups could be matched |
410 | in the pattern, which was the last open paren to be entered, and which was |
411 | the last close paren to be entered. |
412 | |
413 | =item C<intflags> |
414 | |
415 | The engine's private copy of the flags the pattern was compiled with. Usually |
416 | this is the same as C<extflags> unless the engine chose to modify one of them |
417 | |
418 | =item C<pprivate> |
419 | |
420 | A void* pointing to an engine-defined data structure. The perl engine uses the |
421 | C<regexp_internal> structure (see L<perlreguts/Base Structures>) but a custom |
422 | engine should use something else. |
423 | |
424 | =item C<swap> |
425 | |
426 | TODO: document |
427 | |
428 | =item C<offs> |
429 | |
430 | A C<regexp_paren_pair> structure which defines offsets into the string being |
431 | matched which correspond to the C<$&> and C<$1>, C<$2> etc. captures, the |
432 | C<regexp_paren_pair> struct is defined as follows: |
433 | |
434 | typedef struct regexp_paren_pair { |
435 | I32 start; |
436 | I32 end; |
437 | } regexp_paren_pair; |
438 | |
439 | If C<< ->offs[num].start >> or C<< ->offs[num].end >> is C<-1> then that |
440 | capture buffer did not match. C<< ->offs[0].start/end >> represents C<$&> (or |
441 | C<${^MATCH> under C<//p>) and C<< ->offs[paren].end >> matches C<$$paren> where |
442 | C<$paren >= 1>. |
443 | |
444 | =item C<precomp> C<prelen> |
445 | |
446 | Used for debugging purposes. C<precomp> holds a copy of the pattern |
447 | that was compiled and C<prelen> its length. |
448 | |
449 | =item C<paren_names> |
450 | |
451 | This is a hash used internally to track named capture buffers and their |
452 | offsets. The keys are the names of the buffers the values are dualvars, |
453 | with the IV slot holding the number of buffers with the given name and the |
454 | pv being an embedded array of I32. The values may also be contained |
455 | independently in the data array in cases where named backreferences are |
456 | used. |
457 | |
458 | =item C<reg_substr_data> |
459 | |
460 | Holds information on the longest string that must occur at a fixed |
461 | offset from the start of the pattern, and the longest string that must |
462 | occur at a floating offset from the start of the pattern. Used to do |
463 | Fast-Boyer-Moore searches on the string to find out if its worth using |
464 | the regex engine at all, and if so where in the string to search. |
465 | |
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466 | =item C<subbeg> C<sublen> C<saved_copy> |
467 | |
468 | #define SAVEPVN(p,n) ((p) ? savepvn(p,n) : NULL) |
469 | if (RX_MATCH_COPIED(ret)) |
470 | ret->subbeg = SAVEPVN(ret->subbeg, ret->sublen); |
471 | else |
472 | ret->subbeg = NULL; |
473 | |
474 | C<PL_sawampersand || rx->extflags & RXf_PMf_KEEPCOPY> |
475 | |
476 | These are used during execution phase for managing search and replace |
477 | patterns. |
478 | |
479 | =item C<wrapped> C<wraplen> |
480 | |
481 | Stores the string C<qr//> stringifies to, for example C<(?-xism:eek)> |
482 | in the case of C<qr/eek/>. |
483 | |
484 | When using a custom engine that doesn't support the C<(?:)> construct for |
485 | inline modifiers it's best to have C<qr//> stringify to the supplied pattern, |
486 | note that this will create invalid patterns in cases such as: |
487 | |
488 | my $x = qr/a|b/; # "a|b" |
489 | my $y = qr/c/; # "c" |
490 | my $z = qr/$x$y/; # "a|bc" |
491 | |
492 | There's no solution for such problems other than making the custom engine |
493 | understand some for of inline modifiers. |
494 | |
495 | The C<Perl_reg_stringify> in F<regcomp.c> does the stringification work. |
496 | |
497 | =item C<seen_evals> |
498 | |
499 | This stores the number of eval groups in the pattern. This is used for security |
500 | purposes when embedding compiled regexes into larger patterns with C<qr//>. |
501 | |
502 | =item C<refcnt> |
503 | |
504 | The number of times the structure is referenced. When this falls to 0 the |
505 | regexp is automatically freed by a call to pregfree. This should be set to 1 in |
506 | each engine's L</comp> routine. |
507 | |
508 | =back |
509 | |
510 | =head2 De-allocation and Cloning |
511 | |
512 | Any patch that adds data items to the REGEXP struct will need to include |
513 | changes to F<sv.c> (C<Perl_re_dup()>) and F<regcomp.c> (C<pregfree()>). This |
514 | involves freeing or cloning items in the regexp's data array based on the data |
515 | item's type. |
516 | |
517 | =head1 HISTORY |
518 | |
519 | Originally part of L<perlreguts>. |
520 | |
521 | =head1 AUTHORS |
522 | |
523 | Originally written by Yves Orton, expanded by E<AElig>var ArnfjE<ouml>rE<eth> |
524 | Bjarmason. |
525 | |
526 | =head1 LICENSE |
527 | |
528 | Copyright 2006 Yves Orton and 2007 E<AElig>var ArnfjE<ouml>rE<eth> Bjarmason. |
529 | |
530 | This program is free software; you can redistribute it and/or modify it under |
531 | the same terms as Perl itself. |
532 | |
533 | =cut |