ExtUtils::Constant::Base
ExtUtils::Constant::BasPerl Programmers Reference ExtUtils::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, typi-
cally 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 aggre-
gate (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 num-
ber 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 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_defi-
nition 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.
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 refer-
ence 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 fol-
lowed 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 tem-
porary) 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 parame-
ters 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 v5.8.8 2001-09-21 ExtUtils::Constant::Base(3)
