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       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 highlight the position of the character in the "switch"

           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 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 cannot be inferred from default_types and the

       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 without 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
           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 C_constant_other_params

       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.

       normalise_items args, default_type, seen_types, seen_items, ITEM...
           Convert the items to a normalised form. For 8 bit and Unicode
           values converts the item to an array of 1 or 2 items, both 8 bit
           and UTF-8 encoded.

       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 constructions 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 generated 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 information 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 v5.24.0                      2015-10-14     ExtUtils::Constant::Base(3pm)

perl 5.24 - Generated Tue Nov 8 15:12:30 CST 2016
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