MirBSD manpage: ExtUtils::Constant::Base(3p)

ExtUtils::ConstanPerlaProgrammers RefExtUtils::Constant::Base(3p)


     ExtUtils::Constant::Base - base class for ExtUtils::Constant


         require ExtUtils::Constant::Base;
         @ISA = 'ExtUtils::Constant::Base';


     ExtUtils::Constant::Base provides a base implementation of
     methods to generate C code to give fast constant value
     lookup by named string. Currently it's mostly used
     ExtUtils::Constant::XS, which generates the lookup code for
     the constant() subroutine found in many XS modules.


     ExtUtils::Constant::Base exports no subroutines. The follow-
     ing methods are available

         A method returning a scalar containing definitions
         needed, typically for a C header file.

     memEQ_clause args_hashref
         A method to return a suitable C "if" statement to check
         whether name is equal to the C variable "name". If
         checked_at is defined, then it is used to avoid "memEQ"
         for short names, or to generate a comment to highlight
         the position of the character in the "switch" statement.

         If i<checked_at> is a reference to a scalar, then
         instead it gives the characters pre-checked at the
         beginning, (and the number of chars by which the C vari-
         able name has been advanced. These need to be chopped
         from the front of name).

     dump_names arg_hashref, ITEM...
         An internal function to generate the embedded perl code
         that will regenerate the constant subroutines.
         default_type, types and ITEMs are the same as for
         C_constant.  indent is treated as number of spaces to
         indent by.  If "declare_types" is true a $types is
         always declared in the perl code generated, if defined
         and false never declared, and if undefined $types is
         only declared if the values in types as passed in cannot
         be inferred from default_types and the ITEMs.

     assign arg_hashref, VALUE...
         A method to return a suitable assignment clause. If type
         is aggregate (eg PVN expects both pointer and length)
         then there should be multiple VALUEs for the components.
         pre and post if defined give snippets of C code to

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         proceed and follow the assignment. pre will be at the
         start of a block, so variables may be defined in it.

     return_clause arg_hashref, ITEM
         A method to return a suitable "#ifdef" clause. ITEM is a
         hashref (as passed to "C_constant" and "match_clause".
         indent is the number of spaces to indent, defaulting to

     switch_clause arg_hashref, NAMELEN, ITEMHASH, ITEM...
         An internal method to generate a suitable "switch"
         clause, called by "C_constant" ITEMs are in the hash ref
         format as given in the description of "C_constant", and
         must all have the names of the same length, given by
         NAMELEN.  ITEMHASH is a reference to a hash, keyed by
         name, values being the hashrefs in the ITEM list.  (No
         parameters are modified, and there can be keys in the
         ITEMHASH that are not in the list of ITEMs without caus-
         ing problems - the hash is passed in to save generating
         it afresh for each call).

     params WHAT
         An "internal" method, subject to change, currently
         called to allow an overriding class to cache information
         that will then be passed into all the "*param*" calls.
         (Yes, having to read the source to make sense of this is
         considered a known bug). WHAT is be a hashref of types
         the constant function will return. In
         ExtUtils::Constant::XS this method is used to returns a
         hashref keyed IV NV PV SV to show which combination of
         pointers will be needed in the C argument list generated
         by C_constant_other_params_definition and

     dogfood arg_hashref, ITEM...
         An internal function to generate the embedded perl code
         that will regenerate the constant subroutines.  Parame-
         ters are the same as for C_constant.

         Currently the base class does nothing and returns an
         empty string.

     C_constant arg_hashref, ITEM...
         A function that returns a list of C subroutine defini-
         tions that return the value and type of constants when
         passed the name by the XS wrapper. ITEM... gives a list
         of constant names. Each can either be a string, which is
         taken as a C macro name, or a reference to a hash with
         the following keys

         name    The name of the constant, as seen by the perl

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         type    The type of the constant (IV, NV etc)

         value   A C expression for the value of the constant, or
                 a list of C expressions if the type is aggre-
                 gate. This defaults to the name if not given.

         macro   The C pre-processor macro to use in the
                 "#ifdef". This defaults to the name, and is
                 mainly used if value is an "enum". If a refer-
                 ence an array is passed then the first element
                 is used in place of the "#ifdef" line, and the
                 second element in place of the "#endif". This
                 allows pre-processor constructions such as

                     #if defined (foo)
                     #if !defined (bar)

                 to be used to determine if a constant is to be

                 A "macro" 1 signals that the constant is always
                 defined, so the "#if"/"#endif" test is omitted.

         default Default value to use (instead of "croak"ing with
                 "your vendor has not defined...") to return if
                 the macro isn't defined. Specify a reference to
                 an array with type followed by value(s).

         pre     C code to use before the assignment of the value
                 of the constant. This allows you to use tem-
                 porary variables to extract a value from part of
                 a "struct" and return this as value. This C code
                 is places at the start of a block, so you can
                 declare variables in it.

         post    C code to place between the assignment of value
                 (to a temporary) and the return from the func-
                 tion. This allows you to clear up anything in
                 pre. Rarely needed.

                 Equivalents of pre and post for the default

         utf8    Generated internally. Is zero or undefined if
                 name is 7 bit ASCII, "no" if the name is 8 bit
                 (and so should only match if SvUTF8() is false),
                 "yes" if the name is utf8 encoded.

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                 The internals automatically clone any name with
                 characters 128-255 but none 256+ (ie one that
                 could be either in bytes or utf8) into a second
                 entry which is utf8 encoded.

         weight  Optional sorting weight for names, to determine
                 the order of linear testing when multiple names
                 fall in the same case of a switch clause. Higher
                 comes earlier, undefined defaults to zero.

         In the argument hashref, package is the name of the
         package, and is only used in comments inside the gen-
         erated C code. subname defaults to "constant" if unde-

         default_type is the type returned by "ITEM"s that don't
         specify their type. It defaults to the value of
         "default_type()". types should be given either as a
         comma separated list of types that the C subroutine sub-
         name will generate or as a reference to a hash.
         default_type will be added to the list if not present,
         as will any types given in the list of ITEMs. The resul-
         tant list should be the same list of types that
         "XS_constant" is given. [Otherwise "XS_constant" and
         "C_constant" may differ in the number of parameters to
         the constant function. indent is currently unused and
         ignored. In future it may be used to pass in information
         used to change the C indentation style used.]  The best
         way to maintain consistency is to pass in a hash refer-
         ence and let this function update it.

         breakout governs when child functions of subname are
         generated.  If there are breakout or more ITEMs with the
         same length of name, then the code to switch between
         them is placed into a function named subname_len, for
         example "constant_5" for names 5 characters long.  The
         default breakout is 3.  A single "ITEM" is always


     Not everything is documented yet.

     Probably others.


     Nicholas Clark <nick@ccl4.org> based on the code in "h2xs"
     by Larry Wall and others

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