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