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129 | .\" ======================================================================== | |
130 | .\" | |
131 | .IX Title "ExtUtils::Constant::Base 3" | |
132 | .TH ExtUtils::Constant::Base 3 "2001-09-21" "perl v5.8.8" "Perl Programmers Reference Guide" | |
133 | .SH "NAME" | |
134 | ExtUtils::Constant::Base \- base class for ExtUtils::Constant objects | |
135 | .SH "SYNOPSIS" | |
136 | .IX Header "SYNOPSIS" | |
137 | .Vb 2 | |
138 | \& require ExtUtils::Constant::Base; | |
139 | \& @ISA = 'ExtUtils::Constant::Base'; | |
140 | .Ve | |
141 | .SH "DESCRIPTION" | |
142 | .IX Header "DESCRIPTION" | |
143 | ExtUtils::Constant::Base provides a base implementation of methods to | |
144 | generate C code to give fast constant value lookup by named string. Currently | |
145 | it's mostly used ExtUtils::Constant::XS, which generates the lookup code | |
146 | for the \fIconstant()\fR subroutine found in many \s-1XS\s0 modules. | |
147 | .SH "USAGE" | |
148 | .IX Header "USAGE" | |
149 | ExtUtils::Constant::Base exports no subroutines. The following methods are | |
150 | available | |
151 | .IP "header" 4 | |
152 | .IX Item "header" | |
153 | A method returning a scalar containing definitions needed, typically for a | |
154 | C header file. | |
155 | .IP "memEQ_clause args_hashref" 4 | |
156 | .IX Item "memEQ_clause args_hashref" | |
157 | A method to return a suitable C \f(CW\*(C`if\*(C'\fR statement to check whether \fIname\fR | |
158 | is equal to the C variable \f(CW\*(C`name\*(C'\fR. If \fIchecked_at\fR is defined, then it | |
159 | is used to avoid \f(CW\*(C`memEQ\*(C'\fR for short names, or to generate a comment to | |
160 | highlight the position of the character in the \f(CW\*(C`switch\*(C'\fR statement. | |
161 | .Sp | |
162 | If i<checked_at> is a reference to a scalar, then instead it gives | |
163 | the characters pre-checked at the beginning, (and the number of chars by | |
164 | which the C variable name has been advanced. These need to be chopped from | |
165 | the front of \fIname\fR). | |
166 | .IP "dump_names arg_hashref, \s-1ITEM\s0..." 4 | |
167 | .IX Item "dump_names arg_hashref, ITEM..." | |
168 | An internal function to generate the embedded perl code that will regenerate | |
169 | the constant subroutines. \fIdefault_type\fR, \fItypes\fR and \fI\s-1ITEM\s0\fRs are the | |
170 | same as for C_constant. \fIindent\fR is treated as number of spaces to indent | |
171 | by. If \f(CW\*(C`declare_types\*(C'\fR is true a \f(CW$types\fR is always declared in the perl | |
172 | code generated, if defined and false never declared, and if undefined \f(CW$types\fR | |
173 | is only declared if the values in \fItypes\fR as passed in cannot be inferred from | |
174 | \&\fIdefault_types\fR and the \fI\s-1ITEM\s0\fRs. | |
175 | .IP "assign arg_hashref, \s-1VALUE\s0..." 4 | |
176 | .IX Item "assign arg_hashref, VALUE..." | |
177 | A method to return a suitable assignment clause. If \fItype\fR is aggregate | |
178 | (eg \fI\s-1PVN\s0\fR expects both pointer and length) then there should be multiple | |
179 | \&\fI\s-1VALUE\s0\fRs for the components. \fIpre\fR and \fIpost\fR if defined give snippets | |
180 | of C code to proceed and follow the assignment. \fIpre\fR will be at the start | |
181 | of a block, so variables may be defined in it. | |
182 | .IP "return_clause arg_hashref, \s-1ITEM\s0" 4 | |
183 | .IX Item "return_clause arg_hashref, ITEM" | |
184 | A method to return a suitable \f(CW\*(C`#ifdef\*(C'\fR clause. \fI\s-1ITEM\s0\fR is a hashref | |
185 | (as passed to \f(CW\*(C`C_constant\*(C'\fR and \f(CW\*(C`match_clause\*(C'\fR. \fIindent\fR is the number | |
186 | of spaces to indent, defaulting to 6. | |
187 | .IP "switch_clause arg_hashref, \s-1NAMELEN\s0, \s-1ITEMHASH\s0, \s-1ITEM\s0..." 4 | |
188 | .IX Item "switch_clause arg_hashref, NAMELEN, ITEMHASH, ITEM..." | |
189 | An internal method to generate a suitable \f(CW\*(C`switch\*(C'\fR clause, called by | |
190 | \&\f(CW\*(C`C_constant\*(C'\fR \fI\s-1ITEM\s0\fRs are in the hash ref format as given in the description | |
191 | of \f(CW\*(C`C_constant\*(C'\fR, and must all have the names of the same length, given by | |
192 | \&\fI\s-1NAMELEN\s0\fR. \fI\s-1ITEMHASH\s0\fR is a reference to a hash, keyed by name, values being | |
193 | the hashrefs in the \fI\s-1ITEM\s0\fR list. (No parameters are modified, and there can | |
194 | be keys in the \fI\s-1ITEMHASH\s0\fR that are not in the list of \fI\s-1ITEM\s0\fRs without | |
195 | causing problems \- the hash is passed in to save generating it afresh for | |
196 | each call). | |
197 | .IP "params \s-1WHAT\s0" 4 | |
198 | .IX Item "params WHAT" | |
199 | An \*(L"internal\*(R" method, subject to change, currently called to allow an | |
200 | overriding class to cache information that will then be passed into all | |
201 | the \f(CW\*(C`*param*\*(C'\fR calls. (Yes, having to read the source to make sense of this is | |
202 | considered a known bug). \fI\s-1WHAT\s0\fR is be a hashref of types the constant | |
203 | function will return. In ExtUtils::Constant::XS this method is used to | |
204 | returns a hashref keyed \s-1IV\s0 \s-1NV\s0 \s-1PV\s0 \s-1SV\s0 to show which combination of pointers will | |
205 | be needed in the C argument list generated by | |
206 | C_constant_other_params_definition and C_constant_other_params | |
207 | .IP "dogfood arg_hashref, \s-1ITEM\s0..." 4 | |
208 | .IX Item "dogfood arg_hashref, ITEM..." | |
209 | An internal function to generate the embedded perl code that will regenerate | |
210 | the constant subroutines. Parameters are the same as for C_constant. | |
211 | .Sp | |
212 | Currently the base class does nothing and returns an empty string. | |
213 | .IP "C_constant arg_hashref, \s-1ITEM\s0..." 4 | |
214 | .IX Item "C_constant arg_hashref, ITEM..." | |
215 | A function that returns a \fBlist\fR of C subroutine definitions that return | |
216 | the value and type of constants when passed the name by the \s-1XS\s0 wrapper. | |
217 | \&\fI\s-1ITEM\s0...\fR gives a list of constant names. Each can either be a string, | |
218 | which is taken as a C macro name, or a reference to a hash with the following | |
219 | keys | |
220 | .RS 4 | |
221 | .IP "name" 8 | |
222 | .IX Item "name" | |
223 | The name of the constant, as seen by the perl code. | |
224 | .IP "type" 8 | |
225 | .IX Item "type" | |
226 | The type of the constant (\fI\s-1IV\s0\fR, \fI\s-1NV\s0\fR etc) | |
227 | .IP "value" 8 | |
228 | .IX Item "value" | |
229 | A C expression for the value of the constant, or a list of C expressions if | |
230 | the type is aggregate. This defaults to the \fIname\fR if not given. | |
231 | .IP "macro" 8 | |
232 | .IX Item "macro" | |
233 | The C pre-processor macro to use in the \f(CW\*(C`#ifdef\*(C'\fR. This defaults to the | |
234 | \&\fIname\fR, and is mainly used if \fIvalue\fR is an \f(CW\*(C`enum\*(C'\fR. If a reference an | |
235 | array is passed then the first element is used in place of the \f(CW\*(C`#ifdef\*(C'\fR | |
236 | line, and the second element in place of the \f(CW\*(C`#endif\*(C'\fR. This allows | |
237 | pre-processor constructions such as | |
238 | .Sp | |
239 | .Vb 5 | |
240 | \& #if defined (foo) | |
241 | \& #if !defined (bar) | |
242 | \& ... | |
243 | \& #endif | |
244 | \& #endif | |
245 | .Ve | |
246 | .Sp | |
247 | to be used to determine if a constant is to be defined. | |
248 | .Sp | |
249 | A \*(L"macro\*(R" 1 signals that the constant is always defined, so the \f(CW\*(C`#if\*(C'\fR/\f(CW\*(C`#endif\*(C'\fR | |
250 | test is omitted. | |
251 | .IP "default" 8 | |
252 | .IX Item "default" | |
253 | Default value to use (instead of \f(CW\*(C`croak\*(C'\fRing with \*(L"your vendor has not | |
254 | defined...\*(R") to return if the macro isn't defined. Specify a reference to | |
255 | an array with type followed by value(s). | |
256 | .IP "pre" 8 | |
257 | .IX Item "pre" | |
258 | C code to use before the assignment of the value of the constant. This allows | |
259 | you to use temporary variables to extract a value from part of a \f(CW\*(C`struct\*(C'\fR | |
260 | and return this as \fIvalue\fR. This C code is places at the start of a block, | |
261 | so you can declare variables in it. | |
262 | .IP "post" 8 | |
263 | .IX Item "post" | |
264 | C code to place between the assignment of value (to a temporary) and the | |
265 | return from the function. This allows you to clear up anything in \fIpre\fR. | |
266 | Rarely needed. | |
267 | .IP "def_pre" 8 | |
268 | .IX Item "def_pre" | |
269 | .PD 0 | |
270 | .IP "def_post" 8 | |
271 | .IX Item "def_post" | |
272 | .PD | |
273 | Equivalents of \fIpre\fR and \fIpost\fR for the default value. | |
274 | .IP "utf8" 8 | |
275 | .IX Item "utf8" | |
276 | Generated internally. Is zero or undefined if name is 7 bit \s-1ASCII\s0, | |
277 | \&\*(L"no\*(R" if the name is 8 bit (and so should only match if \fISvUTF8()\fR is false), | |
278 | \&\*(L"yes\*(R" if the name is utf8 encoded. | |
279 | .Sp | |
280 | The internals automatically clone any name with characters 128\-255 but none | |
281 | 256+ (ie one that could be either in bytes or utf8) into a second entry | |
282 | which is utf8 encoded. | |
283 | .IP "weight" 8 | |
284 | .IX Item "weight" | |
285 | Optional sorting weight for names, to determine the order of | |
286 | linear testing when multiple names fall in the same case of a switch clause. | |
287 | Higher comes earlier, undefined defaults to zero. | |
288 | .RE | |
289 | .RS 4 | |
290 | .Sp | |
291 | In the argument hashref, \fIpackage\fR is the name of the package, and is only | |
292 | used in comments inside the generated C code. \fIsubname\fR defaults to | |
293 | \&\f(CW\*(C`constant\*(C'\fR if undefined. | |
294 | .Sp | |
295 | \&\fIdefault_type\fR is the type returned by \f(CW\*(C`ITEM\*(C'\fRs that don't specify their | |
296 | type. It defaults to the value of \f(CW\*(C`default_type()\*(C'\fR. \fItypes\fR should be given | |
297 | either as a comma separated list of types that the C subroutine \fIsubname\fR | |
298 | will generate or as a reference to a hash. \fIdefault_type\fR will be added to | |
299 | the list if not present, as will any types given in the list of \fI\s-1ITEM\s0\fRs. The | |
300 | resultant list should be the same list of types that \f(CW\*(C`XS_constant\*(C'\fR is | |
301 | given. [Otherwise \f(CW\*(C`XS_constant\*(C'\fR and \f(CW\*(C`C_constant\*(C'\fR may differ in the number of | |
302 | parameters to the constant function. \fIindent\fR is currently unused and | |
303 | ignored. In future it may be used to pass in information used to change the C | |
304 | indentation style used.] The best way to maintain consistency is to pass in a | |
305 | hash reference and let this function update it. | |
306 | .Sp | |
307 | \&\fIbreakout\fR governs when child functions of \fIsubname\fR are generated. If there | |
308 | are \fIbreakout\fR or more \fI\s-1ITEM\s0\fRs with the same length of name, then the code | |
309 | to switch between them is placed into a function named \fIsubname\fR_\fIlen\fR, for | |
310 | example \f(CW\*(C`constant_5\*(C'\fR for names 5 characters long. The default \fIbreakout\fR is | |
311 | 3. A single \f(CW\*(C`ITEM\*(C'\fR is always inlined. | |
312 | .RE | |
313 | .SH "BUGS" | |
314 | .IX Header "BUGS" | |
315 | Not everything is documented yet. | |
316 | .PP | |
317 | Probably others. | |
318 | .SH "AUTHOR" | |
319 | .IX Header "AUTHOR" | |
320 | Nicholas Clark <nick@ccl4.org> based on the code in \f(CW\*(C`h2xs\*(C'\fR by Larry Wall and | |
321 | others |