ExtUtils::ConstanPerlaProgrammers RefExtUtils::Constant::Base(3p)NAMEExtUtils::Constant::Base - base class for ExtUtils::Constant
objects
SYNOPSIS
require ExtUtils::Constant::Base;
@ISA = 'ExtUtils::Constant::Base';
DESCRIPTIONExtUtils::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.
USAGEExtUtils::Constant::Base exports no subroutines. The follow-
ing 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 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
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 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
C_constant_other_params
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
code.
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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)
...
#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 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.
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.
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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-
fined.
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
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
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