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

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

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

DESCRIPTION
       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.

USAGE
       ExtUtils::Constant::Base exports no subroutines. The following methods
       are available

       header
	   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 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
	   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 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)
		       ...
		       #endif
		       #endif

		   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.

	   def_pre
	   def_post
		   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.

BUGS
       Not everything is documented yet.

       Probably others.

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

perl v5.10.0			  2007-12-18	   ExtUtils::Constant::Base(3)
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