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ExtUtils::Constant::BasPerl Programmers Reference GExtUtils::Constant::Base(3)

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

           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 following 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 high-
           light 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 begin-
           ning, (and the number of chars by which the C variable 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 can-
           not 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 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 6.

       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 with-
           out causing 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 ExtU-
           tils::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 C_con-

       dogfood arg_hashref, ITEM...
           An internal function to generate the embedded perl code that will regenerate the constant subroutines.
           Parameters 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 definitions 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 code.

           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 aggregate.
                   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 reference 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 con-
                   structions such as

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

                   to be used to determine if a constant is to be defined.

                   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 temporary
                   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 function.
                   This allows you to clear up anything in pre.  Rarely needed.

                   Equivalents of pre and post for the default value.

           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.

                   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 gener-
           ated C code. subname defaults to "constant" if undefined.

           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
           subname 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 resultant 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 informa-
           tion used to change the C indentation style used.]  The best way to maintain consistency is to pass in a
           hash reference 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 inlined.

       Not everything is documented yet.

       Probably others.

       Nicholas Clark <> based on the code in "h2xs" by Larry Wall and others

perl v5.8.8                       2001-09-21       ExtUtils::Constant::Base(3)