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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 |