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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, |
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14 | char* strbeg, I32 minend, SV* screamer, |
15 | void* data, U32 flags); |
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16 | char* (*intuit) (pTHX_ REGEXP * const rx, SV *sv, char *strpos, |
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17 | char *strend, U32 flags, |
18 | struct re_scream_pos_data_s *data); |
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19 | SV* (*checkstr) (pTHX_ REGEXP * const rx); |
20 | void (*free) (pTHX_ REGEXP * const rx); |
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21 | void (*numbered_buff_FETCH) (pTHX_ REGEXP * const rx, const I32 paren, |
22 | SV * const sv); |
23 | void (*numbered_buff_STORE) (pTHX_ REGEXP * const rx, const I32 paren, |
24 | SV const * const value); |
25 | I32 (*numbered_buff_LENGTH) (pTHX_ REGEXP * const rx, const SV * const sv, |
26 | const I32 paren); |
27 | SV* (*named_buff_FETCH) (pTHX_ REGEXP * const rx, SV * const sv, |
28 | const U32 flags); |
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29 | SV* (*qr_package)(pTHX_ REGEXP * const rx); |
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30 | #ifdef USE_ITHREADS |
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31 | void* (*dupe) (pTHX_ REGEXP * const rx, CLONE_PARAMS *param); |
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32 | #endif |
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33 | |
34 | When a regexp is compiled, its C<engine> field is then set to point at |
35 | the appropriate structure so that when it needs to be used Perl can find |
36 | the right routines to do so. |
37 | |
38 | In order to install a new regexp handler, C<$^H{regcomp}> is set |
39 | to an integer which (when casted appropriately) resolves to one of these |
40 | structures. When compiling, the C<comp> method is executed, and the |
41 | resulting regexp structure's engine field is expected to point back at |
42 | the same structure. |
43 | |
44 | The pTHX_ symbol in the definition is a macro used by perl under threading |
45 | to provide an extra argument to the routine holding a pointer back to |
46 | the interpreter that is executing the regexp. So under threading all |
47 | routines get an extra argument. |
48 | |
49 | The routines are as follows: |
50 | |
51 | =head2 comp |
52 | |
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53 | REGEXP* comp(pTHX_ const SV * const pattern, const U32 flags); |
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54 | |
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55 | Compile the pattern stored in C<pattern> using the given C<flags> and |
56 | return a pointer to a prepared C<REGEXP> structure that can perform |
57 | the match. See L</The REGEXP structure> below for an explanation of |
58 | the individual fields in the REGEXP struct. |
59 | |
60 | The C<pattern> parameter is the scalar that was used as the |
61 | pattern. previous versions of perl would pass two C<char*> indicating |
62 | the start and end of the stringifed pattern, the following snippet can |
63 | be used to get the old parameters: |
64 | |
65 | STRLEN plen; |
66 | char* exp = SvPV(pattern, plen); |
67 | char* xend = exp + plen; |
68 | |
69 | Since any scalar can be passed as a pattern it's possible to implement |
70 | an engine that does something with an array (C<< "ook" =~ [ qw/ eek |
71 | hlagh / ] >>) or with the non-stringified form of a compiled regular |
72 | expression (C<< "ook" =~ qr/eek/ >>). perl's own engine will always |
73 | stringify everything using the snippet above but that doesn't mean |
74 | other engines have to. |
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75 | |
76 | The C<flags> paramater is a bitfield which indicates which of the |
77 | C<msixk> flags the regex was compiled with. In addition it contains |
78 | info about whether C<use locale> is in effect and optimization info |
79 | for C<split>. A regex engine might want to use the same split |
80 | optimizations with a different syntax, for instance a Perl6 engine |
81 | would treat C<split /^^/> equivalently to perl's C<split /^/>, see |
82 | L<split documentation|perlfunc> and the relevant code in C<pp_split> |
83 | in F<pp.c> to find out whether your engine should be setting these. |
84 | |
85 | The C<eogc> flags are stripped out before being passed to the comp |
86 | routine. The regex engine does not need to know whether any of these |
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87 | are set as those flags should only affect what perl does with the |
88 | pattern and its match variables, not how it gets compiled & executed. |
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89 | |
90 | =over 4 |
91 | |
92 | =item RXf_SKIPWHITE |
93 | |
94 | C<split ' '> or C<split> with no arguments (which really means |
95 | C<split(' ', $_> see L<split|perlfunc>). |
96 | |
97 | =item RXf_START_ONLY |
98 | |
99 | Set if the pattern is C</^/> (C<<r->prelen == 1 && r->precomp[0] == |
100 | '^'>>). Will be used by the C<split> operator to split the given |
101 | string on C<\n> (even under C</^/s>, see L<split|perlfunc>). |
102 | |
103 | =item RXf_WHITE |
104 | |
105 | Set if the pattern is exactly C</\s+/> and used by C<split>, the |
106 | definition of whitespace varies depending on whether RXf_UTF8 or |
107 | RXf_PMf_LOCALE is set. |
108 | |
109 | =item RXf_PMf_LOCALE |
110 | |
111 | Makes C<split> use the locale dependant definition of whitespace under C<use |
112 | locale> when RXf_SKIPWHITE or RXf_WHITE is in effect. Under ASCII whitespace is |
113 | defined as per L<isSPACE|perlapi/ISSPACE>, and by the internal macros |
114 | C<is_utf8_space> under UTF-8 and C<isSPACE_LC> under C<use locale>. |
115 | |
116 | =item RXf_PMf_MULTILINE |
117 | |
118 | The C</m> flag, this ends up being passed to C<Perl_fbm_instr> by |
119 | C<pp_split> regardless of the engine. |
120 | |
121 | =item RXf_PMf_SINGLELINE |
122 | |
123 | The C</s> flag. Guaranteed not to be used outside the regex engine. |
124 | |
125 | =item RXf_PMf_FOLD |
126 | |
127 | The C</i> flag. Guaranteed not to be used outside the regex engine. |
128 | |
129 | =item RXf_PMf_EXTENDED |
130 | |
131 | The C</x> flag. Guaranteed not to be used outside the regex |
132 | engine. However if present on a regex C<#> comments will be stripped |
133 | by the tokenizer regardless of the engine currently in use. |
134 | |
135 | =item RXf_PMf_KEEPCOPY |
136 | |
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137 | The C</p> flag. |
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138 | |
139 | =item RXf_UTF8 |
140 | |
141 | Set if the pattern is L<SvUTF8()|perlapi/SvUTF8>, set by Perl_pmruntime. |
142 | |
143 | =back |
144 | |
145 | In general these flags should be preserved in regex->extflags after |
146 | compilation, although it is possible the regex includes constructs |
147 | that changes them. The perl engine for instance may upgrade non-utf8 |
148 | strings to utf8 if the pattern includes constructs such as C<\x{...}> |
149 | that can only match unicode values. RXf_SKIPWHITE should always be |
150 | preserved verbatim in regex->extflags. |
151 | |
152 | =head2 exec |
153 | |
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154 | I32 exec(pTHX_ REGEXP * const rx, |
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155 | char *stringarg, char* strend, char* strbeg, |
156 | I32 minend, SV* screamer, |
157 | void* data, U32 flags); |
158 | |
159 | Execute a regexp. |
160 | |
161 | =head2 intuit |
162 | |
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163 | char* intuit(pTHX_ REGEXP * const rx, |
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164 | SV *sv, char *strpos, char *strend, |
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165 | const U32 flags, struct re_scream_pos_data_s *data); |
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166 | |
167 | Find the start position where a regex match should be attempted, |
168 | or possibly whether the regex engine should not be run because the |
169 | pattern can't match. This is called as appropriate by the core |
170 | depending on the values of the extflags member of the regexp |
171 | structure. |
172 | |
173 | =head2 checkstr |
174 | |
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175 | SV* checkstr(pTHX_ REGEXP * const rx); |
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176 | |
177 | Return a SV containing a string that must appear in the pattern. Used |
178 | by C<split> for optimising matches. |
179 | |
180 | =head2 free |
181 | |
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182 | void free(pTHX_ REGEXP * const rx); |
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183 | |
184 | Called by perl when it is freeing a regexp pattern so that the engine |
185 | can release any resources pointed to by the C<pprivate> member of the |
186 | regexp structure. This is only responsible for freeing private data; |
187 | perl will handle releasing anything else contained in the regexp structure. |
188 | |
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189 | =head2 numbered_buff_FETCH |
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190 | |
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191 | void numbered_buff_FETCH(pTHX_ REGEXP * const rx, const I32 paren, |
192 | SV * const sv); |
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193 | |
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194 | Called to get the value of C<$`>, C<$'>, C<$&> (and their named |
195 | equivalents, see L<perlvar>) and the numbered capture buffers (C<$1>, |
196 | C<$2>, ...). |
197 | |
198 | The C<paren> paramater will be C<-2> for C<$`>, C<-1> for C<$'>, C<0> |
199 | for C<$&>, C<1> for C<$1> and so forth. |
200 | |
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201 | C<sv> should be set to the scalar to return, the scalar is passed as |
202 | an argument rather than being returned from the function because when |
203 | it's called perl already has a scalar to store the value, creating |
204 | another one would be redundant. The scalar can be set with |
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205 | C<sv_setsv>, C<sv_setpvn> and friends, see L<perlapi>. |
206 | |
207 | This callback is where perl untaints its own capture variables under |
208 | taint mode (see L<perlsec>). See the C<Perl_reg_numbered_buff_get> |
209 | function in F<regcomp.c> for how to untaint capture variables if |
210 | that's something you'd like your engine to do as well. |
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211 | |
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212 | =head2 numbered_buff_STORE |
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213 | |
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214 | void (*numbered_buff_STORE) (pTHX_ REGEXP * const rx, const I32 paren, |
215 | SV const * const value); |
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216 | |
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217 | Called to set the value of a numbered capture variable. C<paren> is |
218 | the paren number (see the L<mapping|/numbered_buff_FETCH> above) and |
219 | C<value> is the scalar that is to be used as the new value. It's up to |
220 | the engine to make sure this is used as the new value (or reject it). |
221 | |
222 | Example: |
223 | |
224 | if ("ook" =~ /(o*)/) { |
225 | # `paren' will be `1' and `value' will be `ee' |
226 | $1 =~ tr/o/e/; |
227 | } |
228 | |
229 | Perl's own engine will croak on any attempt to modify the capture |
230 | variables, to do this in another engine use the following callack |
231 | (copied from C<Perl_reg_numbered_buff_store>): |
232 | |
233 | void |
234 | Example_reg_numbered_buff_store(pTHX_ REGEXP * const rx, const I32 paren, |
235 | SV const * const value) |
236 | { |
237 | PERL_UNUSED_ARG(rx); |
238 | PERL_UNUSED_ARG(paren); |
239 | PERL_UNUSED_ARG(value); |
240 | |
241 | if (!PL_localizing) |
242 | Perl_croak(aTHX_ PL_no_modify); |
243 | } |
244 | |
245 | Actually perl 5.10 will not I<always> croak in a statement that looks |
246 | like it would modify a numbered capture variable. This is because the |
247 | STORE callback will not be called if perl can determine that it |
248 | doesn't have to modify the value. This is exactly how tied variables |
249 | behave in the same situation: |
250 | |
251 | package CaptureVar; |
252 | use base 'Tie::Scalar'; |
253 | |
254 | sub TIESCALAR { bless [] } |
255 | sub FETCH { undef } |
256 | sub STORE { die "This doesn't get called" } |
257 | |
258 | package main; |
259 | |
260 | tie my $sv => "CatptureVar"; |
261 | $sv =~ y/a/b/; |
262 | |
263 | Because C<$sv> is C<undef> when the C<y///> operator is applied to it |
264 | the transliteration won't actually execute and the program won't |
265 | C<die>. This is different to how 5.8 behaved since the capture |
266 | variables were READONLY variables then, now they'll just die on |
267 | assignment in the default engine. |
268 | |
269 | =head2 numbered_buff_LENGTH |
270 | |
271 | I32 numbered_buff_LENGTH (pTHX_ REGEXP * const rx, const SV * const sv, |
272 | const I32 paren); |
273 | |
274 | Get the C<length> of a capture variable. There's a special callback |
275 | for this so that perl doesn't have to do a FETCH and run C<length> on |
276 | the result, since the length is (in perl's case) known from a memory |
277 | offset this is much more efficient: |
278 | |
279 | I32 s1 = rx->offs[paren].start; |
280 | I32 s2 = rx->offs[paren].end; |
281 | I32 len = t1 - s1; |
282 | |
283 | This is a little bit more complex in the case of UTF-8, see what |
284 | C<Perl_reg_numbered_buff_length> does with |
285 | L<is_utf8_string_loclen|perlapi/is_utf8_string_loclen>. |
286 | |
287 | =head2 named_buff_FETCH |
288 | |
289 | SV* named_buff_FETCH(pTHX_ REGEXP * const rx, SV * const key, |
290 | const U32 flags); |
291 | |
292 | Called to get the value of key in the C<%+> and C<%-> hashes, C<key> |
293 | is the hash key being requested and if C<flags & 1> is true C<%-> is |
294 | being requested (and C<%+> if it's not). |
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295 | |
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296 | =head2 qr_package |
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297 | |
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298 | SV* qr_package(pTHX_ REGEXP * const rx); |
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299 | |
300 | The package the qr// magic object is blessed into (as seen by C<ref |
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301 | qr//>). It is recommended that engines change this to their package |
302 | name for identification regardless of whether they implement methods |
303 | on the object. |
304 | |
305 | A callback implementation might be: |
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306 | |
307 | SV* |
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308 | Example_reg_qr_package(pTHX_ REGEXP * const rx) |
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309 | { |
310 | PERL_UNUSED_ARG(rx); |
311 | return newSVpvs("re::engine::Example"); |
312 | } |
313 | |
314 | Any method calls on an object created with C<qr//> will be dispatched to the |
315 | package as a normal object. |
316 | |
317 | use re::engine::Example; |
318 | my $re = qr//; |
319 | $re->meth; # dispatched to re::engine::Example::meth() |
320 | |
321 | To retrieve the C<REGEXP> object from the scalar in an XS function use the |
322 | following snippet: |
323 | |
324 | void meth(SV * rv) |
325 | PPCODE: |
326 | MAGIC * mg; |
327 | REGEXP * re; |
328 | |
329 | if (SvMAGICAL(sv)) |
330 | mg_get(sv); |
331 | if (SvROK(sv) && |
332 | (sv = (SV*)SvRV(sv)) && /* assignment deliberate */ |
333 | SvTYPE(sv) == SVt_PVMG && |
334 | (mg = mg_find(sv, PERL_MAGIC_qr))) /* assignment deliberate */ |
335 | { |
336 | re = (REGEXP *)mg->mg_obj; |
337 | } |
338 | |
339 | Or use the (CURRENTLY UNDOCUMENETED!) C<Perl_get_re_arg> function: |
340 | |
341 | void meth(SV * rv) |
342 | PPCODE: |
343 | const REGEXP * const re = (REGEXP *)Perl_get_re_arg( aTHX_ rv, 0, NULL ); |
344 | |
345 | =head2 dupe |
346 | |
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347 | void* dupe(pTHX_ REGEXP * const rx, CLONE_PARAMS *param); |
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348 | |
349 | On threaded builds a regexp may need to be duplicated so that the pattern |
350 | can be used by mutiple threads. This routine is expected to handle the |
351 | duplication of any private data pointed to by the C<pprivate> member of |
352 | the regexp structure. It will be called with the preconstructed new |
353 | regexp structure as an argument, the C<pprivate> member will point at |
354 | the B<old> private structue, and it is this routine's responsibility to |
355 | construct a copy and return a pointer to it (which perl will then use to |
356 | overwrite the field as passed to this routine.) |
357 | |
358 | This allows the engine to dupe its private data but also if necessary |
359 | modify the final structure if it really must. |
360 | |
361 | On unthreaded builds this field doesn't exist. |
362 | |
363 | =head1 The REGEXP structure |
364 | |
365 | The REGEXP struct is defined in F<regexp.h>. All regex engines must be able to |
366 | correctly build such a structure in their L</comp> routine. |
367 | |
368 | The REGEXP structure contains all the data that perl needs to be aware of |
369 | to properly work with the regular expression. It includes data about |
370 | optimisations that perl can use to determine if the regex engine should |
371 | really be used, and various other control info that is needed to properly |
372 | execute patterns in various contexts such as is the pattern anchored in |
373 | some way, or what flags were used during the compile, or whether the |
374 | program contains special constructs that perl needs to be aware of. |
375 | |
376 | In addition it contains two fields that are intended for the private use |
377 | of the regex engine that compiled the pattern. These are the C<intflags> |
378 | and pprivate members. The C<pprivate> is a void pointer to an arbitrary |
379 | structure whose use and management is the responsibility of the compiling |
380 | engine. perl will never modify either of these values. |
381 | |
382 | typedef struct regexp { |
383 | /* what engine created this regexp? */ |
384 | const struct regexp_engine* engine; |
385 | |
386 | /* what re is this a lightweight copy of? */ |
387 | struct regexp* mother_re; |
388 | |
389 | /* Information about the match that the perl core uses to manage things */ |
390 | U32 extflags; /* Flags used both externally and internally */ |
391 | I32 minlen; /* mininum possible length of string to match */ |
392 | I32 minlenret; /* mininum possible length of $& */ |
393 | U32 gofs; /* chars left of pos that we search from */ |
394 | |
395 | /* substring data about strings that must appear |
396 | in the final match, used for optimisations */ |
397 | struct reg_substr_data *substrs; |
398 | |
399 | U32 nparens; /* number of capture buffers */ |
400 | |
401 | /* private engine specific data */ |
402 | U32 intflags; /* Engine Specific Internal flags */ |
403 | void *pprivate; /* Data private to the regex engine which |
404 | created this object. */ |
405 | |
406 | /* Data about the last/current match. These are modified during matching*/ |
407 | U32 lastparen; /* last open paren matched */ |
408 | U32 lastcloseparen; /* last close paren matched */ |
409 | regexp_paren_pair *swap; /* Swap copy of *offs */ |
410 | regexp_paren_pair *offs; /* Array of offsets for (@-) and (@+) */ |
411 | |
412 | char *subbeg; /* saved or original string so \digit works forever. */ |
413 | SV_SAVED_COPY /* If non-NULL, SV which is COW from original */ |
414 | I32 sublen; /* Length of string pointed by subbeg */ |
415 | |
416 | /* Information about the match that isn't often used */ |
417 | I32 prelen; /* length of precomp */ |
418 | const char *precomp; /* pre-compilation regular expression */ |
419 | |
420 | /* wrapped can't be const char*, as it is returned by sv_2pv_flags */ |
421 | char *wrapped; /* wrapped version of the pattern */ |
422 | I32 wraplen; /* length of wrapped */ |
423 | |
424 | I32 seen_evals; /* number of eval groups in the pattern - for security checks */ |
425 | HV *paren_names; /* Optional hash of paren names */ |
426 | |
427 | /* Refcount of this regexp */ |
428 | I32 refcnt; /* Refcount of this regexp */ |
429 | } regexp; |
430 | |
431 | The fields are discussed in more detail below: |
432 | |
433 | =over 4 |
434 | |
435 | =item C<engine> |
436 | |
437 | This field points at a regexp_engine structure which contains pointers |
438 | to the subroutines that are to be used for performing a match. It |
439 | is the compiling routine's responsibility to populate this field before |
440 | returning the regexp object. |
441 | |
442 | Internally this is set to C<NULL> unless a custom engine is specified in |
443 | C<$^H{regcomp}>, perl's own set of callbacks can be accessed in the struct |
444 | pointed to by C<RE_ENGINE_PTR>. |
445 | |
446 | =item C<mother_re> |
447 | |
448 | TODO, see L<http://www.mail-archive.com/perl5-changes@perl.org/msg17328.html> |
449 | |
450 | =item C<extflags> |
451 | |
452 | This will be used by perl to see what flags the regexp was compiled with, this |
453 | will normally be set to the value of the flags parameter on L</comp>. |
454 | |
455 | =item C<minlen> C<minlenret> |
456 | |
457 | The minimum string length required for the pattern to match. This is used to |
458 | prune the search space by not bothering to match any closer to the end of a |
459 | string than would allow a match. For instance there is no point in even |
460 | starting the regex engine if the minlen is 10 but the string is only 5 |
461 | characters long. There is no way that the pattern can match. |
462 | |
463 | C<minlenret> is the minimum length of the string that would be found |
464 | in $& after a match. |
465 | |
466 | The difference between C<minlen> and C<minlenret> can be seen in the |
467 | following pattern: |
468 | |
469 | /ns(?=\d)/ |
470 | |
471 | where the C<minlen> would be 3 but C<minlenret> would only be 2 as the \d is |
472 | required to match but is not actually included in the matched content. This |
473 | distinction is particularly important as the substitution logic uses the |
474 | C<minlenret> to tell whether it can do in-place substition which can result in |
475 | considerable speedup. |
476 | |
477 | =item C<gofs> |
478 | |
479 | Left offset from pos() to start match at. |
480 | |
481 | =item C<substrs> |
482 | |
483 | TODO: document |
484 | |
485 | =item C<nparens>, C<lasparen>, and C<lastcloseparen> |
486 | |
487 | These fields are used to keep track of how many paren groups could be matched |
488 | in the pattern, which was the last open paren to be entered, and which was |
489 | the last close paren to be entered. |
490 | |
491 | =item C<intflags> |
492 | |
493 | The engine's private copy of the flags the pattern was compiled with. Usually |
494 | this is the same as C<extflags> unless the engine chose to modify one of them |
495 | |
496 | =item C<pprivate> |
497 | |
498 | A void* pointing to an engine-defined data structure. The perl engine uses the |
499 | C<regexp_internal> structure (see L<perlreguts/Base Structures>) but a custom |
500 | engine should use something else. |
501 | |
502 | =item C<swap> |
503 | |
504 | TODO: document |
505 | |
506 | =item C<offs> |
507 | |
508 | A C<regexp_paren_pair> structure which defines offsets into the string being |
509 | matched which correspond to the C<$&> and C<$1>, C<$2> etc. captures, the |
510 | C<regexp_paren_pair> struct is defined as follows: |
511 | |
512 | typedef struct regexp_paren_pair { |
513 | I32 start; |
514 | I32 end; |
515 | } regexp_paren_pair; |
516 | |
517 | If C<< ->offs[num].start >> or C<< ->offs[num].end >> is C<-1> then that |
518 | capture buffer did not match. C<< ->offs[0].start/end >> represents C<$&> (or |
519 | C<${^MATCH> under C<//p>) and C<< ->offs[paren].end >> matches C<$$paren> where |
520 | C<$paren >= 1>. |
521 | |
522 | =item C<precomp> C<prelen> |
523 | |
524 | Used for debugging purposes. C<precomp> holds a copy of the pattern |
525 | that was compiled and C<prelen> its length. |
526 | |
527 | =item C<paren_names> |
528 | |
529 | This is a hash used internally to track named capture buffers and their |
530 | offsets. The keys are the names of the buffers the values are dualvars, |
531 | with the IV slot holding the number of buffers with the given name and the |
532 | pv being an embedded array of I32. The values may also be contained |
533 | independently in the data array in cases where named backreferences are |
534 | used. |
535 | |
536 | =item C<reg_substr_data> |
537 | |
538 | Holds information on the longest string that must occur at a fixed |
539 | offset from the start of the pattern, and the longest string that must |
540 | occur at a floating offset from the start of the pattern. Used to do |
541 | Fast-Boyer-Moore searches on the string to find out if its worth using |
542 | the regex engine at all, and if so where in the string to search. |
543 | |
108003db |
544 | =item C<subbeg> C<sublen> C<saved_copy> |
545 | |
546 | #define SAVEPVN(p,n) ((p) ? savepvn(p,n) : NULL) |
547 | if (RX_MATCH_COPIED(ret)) |
548 | ret->subbeg = SAVEPVN(ret->subbeg, ret->sublen); |
549 | else |
550 | ret->subbeg = NULL; |
551 | |
552 | C<PL_sawampersand || rx->extflags & RXf_PMf_KEEPCOPY> |
553 | |
554 | These are used during execution phase for managing search and replace |
555 | patterns. |
556 | |
557 | =item C<wrapped> C<wraplen> |
558 | |
559 | Stores the string C<qr//> stringifies to, for example C<(?-xism:eek)> |
560 | in the case of C<qr/eek/>. |
561 | |
562 | When using a custom engine that doesn't support the C<(?:)> construct for |
563 | inline modifiers it's best to have C<qr//> stringify to the supplied pattern, |
564 | note that this will create invalid patterns in cases such as: |
565 | |
566 | my $x = qr/a|b/; # "a|b" |
567 | my $y = qr/c/; # "c" |
568 | my $z = qr/$x$y/; # "a|bc" |
569 | |
570 | There's no solution for such problems other than making the custom engine |
571 | understand some for of inline modifiers. |
572 | |
573 | The C<Perl_reg_stringify> in F<regcomp.c> does the stringification work. |
574 | |
575 | =item C<seen_evals> |
576 | |
577 | This stores the number of eval groups in the pattern. This is used for security |
578 | purposes when embedding compiled regexes into larger patterns with C<qr//>. |
579 | |
580 | =item C<refcnt> |
581 | |
582 | The number of times the structure is referenced. When this falls to 0 the |
583 | regexp is automatically freed by a call to pregfree. This should be set to 1 in |
584 | each engine's L</comp> routine. |
585 | |
586 | =back |
587 | |
588 | =head2 De-allocation and Cloning |
589 | |
590 | Any patch that adds data items to the REGEXP struct will need to include |
591 | changes to F<sv.c> (C<Perl_re_dup()>) and F<regcomp.c> (C<pregfree()>). This |
592 | involves freeing or cloning items in the regexp's data array based on the data |
593 | item's type. |
594 | |
595 | =head1 HISTORY |
596 | |
597 | Originally part of L<perlreguts>. |
598 | |
599 | =head1 AUTHORS |
600 | |
601 | Originally written by Yves Orton, expanded by E<AElig>var ArnfjE<ouml>rE<eth> |
602 | Bjarmason. |
603 | |
604 | =head1 LICENSE |
605 | |
606 | Copyright 2006 Yves Orton and 2007 E<AElig>var ArnfjE<ouml>rE<eth> Bjarmason. |
607 | |
608 | This program is free software; you can redistribute it and/or modify it under |
609 | the same terms as Perl itself. |
610 | |
611 | =cut |