extutils::constant::base.3

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.\" ========================================================================
.\"
.IX Title "ExtUtils::Constant::Base 3"
.TH ExtUtils::Constant::Base 3 "2007-12-18" "perl v5.10.0" "Perl Programmers Reference Guide"
.\" For nroff, turn off justification.  Always turn off hyphenation; it makes
.\" way too many mistakes in technical documents.
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.nh
.SH "NAME"
ExtUtils::Constant::Base \- base class for ExtUtils::Constant objects
.SH "SYNOPSIS"
.IX Header "SYNOPSIS"
.Vb 2
\&    require ExtUtils::Constant::Base;
\&    @ISA = \*(AqExtUtils::Constant::Base\*(Aq;
.Ve
.SH "DESCRIPTION"
.IX Header "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 \fIconstant()\fR subroutine found in many \s-1XS\s0 modules.
.SH "USAGE"
.IX Header "USAGE"
ExtUtils::Constant::Base exports no subroutines. The following methods are
available
.IP "header" 4
.IX Item "header"
A method returning a scalar containing definitions needed, typically for a
C header file.
.IP "memEQ_clause args_hashref" 4
.IX Item "memEQ_clause args_hashref"
A method to return a suitable C \f(CW\*(C`if\*(C'\fR statement to check whether \fIname\fR
is equal to the C variable \f(CW\*(C`name\*(C'\fR. If \fIchecked_at\fR is defined, then it
is used to avoid \f(CW\*(C`memEQ\*(C'\fR for short names, or to generate a comment to
highlight the position of the character in the \f(CW\*(C`switch\*(C'\fR statement.
.Sp
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 \fIname\fR).
.IP "dump_names arg_hashref, \s-1ITEM\s0..." 4
.IX Item "dump_names arg_hashref, ITEM..."
An internal function to generate the embedded perl code that will regenerate
the constant subroutines.  \fIdefault_type\fR, \fItypes\fR and \fI\s-1ITEM\s0\fRs are the
same as for C_constant.  \fIindent\fR is treated as number of spaces to indent
by.  If \f(CW\*(C`declare_types\*(C'\fR is true a \f(CW$types\fR is always declared in the perl
code generated, if defined and false never declared, and if undefined \f(CW$types\fR
is only declared if the values in \fItypes\fR as passed in cannot be inferred from
\&\fIdefault_types\fR and the \fI\s-1ITEM\s0\fRs.
.IP "assign arg_hashref, \s-1VALUE\s0..." 4
.IX Item "assign arg_hashref, VALUE..."
A method to return a suitable assignment clause. If \fItype\fR is aggregate
(eg \fI\s-1PVN\s0\fR expects both pointer and length) then there should be multiple
\&\fI\s-1VALUE\s0\fRs for the components. \fIpre\fR and \fIpost\fR if defined give snippets
of C code to proceed and follow the assignment. \fIpre\fR will be at the start
of a block, so variables may be defined in it.
.IP "return_clause arg_hashref, \s-1ITEM\s0" 4
.IX Item "return_clause arg_hashref, ITEM"
A method to return a suitable \f(CW\*(C`#ifdef\*(C'\fR clause. \fI\s-1ITEM\s0\fR is a hashref
(as passed to \f(CW\*(C`C_constant\*(C'\fR and \f(CW\*(C`match_clause\*(C'\fR. \fIindent\fR is the number
of spaces to indent, defaulting to 6.
.IP "switch_clause arg_hashref, \s-1NAMELEN\s0, \s-1ITEMHASH\s0, \s-1ITEM\s0..." 4
.IX Item "switch_clause arg_hashref, NAMELEN, ITEMHASH, ITEM..."
An internal method to generate a suitable \f(CW\*(C`switch\*(C'\fR clause, called by
\&\f(CW\*(C`C_constant\*(C'\fR \fI\s-1ITEM\s0\fRs are in the hash ref format as given in the description
of \f(CW\*(C`C_constant\*(C'\fR, and must all have the names of the same length, given by
\&\fI\s-1NAMELEN\s0\fR.  \fI\s-1ITEMHASH\s0\fR is a reference to a hash, keyed by name, values being
the hashrefs in the \fI\s-1ITEM\s0\fR list.  (No parameters are modified, and there can
be keys in the \fI\s-1ITEMHASH\s0\fR that are not in the list of \fI\s-1ITEM\s0\fRs without
causing problems \- the hash is passed in to save generating it afresh for
each call).
.IP "params \s-1WHAT\s0" 4
.IX Item "params WHAT"
An \*(L"internal\*(R" method, subject to change, currently called to allow an
overriding class to cache information that will then be passed into all
the \f(CW\*(C`*param*\*(C'\fR calls. (Yes, having to read the source to make sense of this is
considered a known bug). \fI\s-1WHAT\s0\fR is be a hashref of types the constant
function will return. In ExtUtils::Constant::XS this method is used to
returns a hashref keyed \s-1IV\s0 \s-1NV\s0 \s-1PV\s0 \s-1SV\s0 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
.IP "dogfood arg_hashref, \s-1ITEM\s0..." 4
.IX Item "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.
.Sp
Currently the base class does nothing and returns an empty string.
.IP "normalise_items args, default_type, seen_types, seen_items, \s-1ITEM\s0..." 4
.IX Item "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 \s-1UTF\-8\s0 encoded.
.IP "C_constant arg_hashref, \s-1ITEM\s0..." 4
.IX Item "C_constant arg_hashref, ITEM..."
A function that returns a \fBlist\fR of C subroutine definitions that return
the value and type of constants when passed the name by the \s-1XS\s0 wrapper.
\&\fI\s-1ITEM\s0...\fR 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
.RS 4
.IP "name" 8
.IX Item "name"
The name of the constant, as seen by the perl code.
.IP "type" 8
.IX Item "type"
The type of the constant (\fI\s-1IV\s0\fR, \fI\s-1NV\s0\fR etc)
.IP "value" 8
.IX Item "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 \fIname\fR if not given.
.IP "macro" 8
.IX Item "macro"
The C pre-processor macro to use in the \f(CW\*(C`#ifdef\*(C'\fR. This defaults to the
\&\fIname\fR, and is mainly used if \fIvalue\fR is an \f(CW\*(C`enum\*(C'\fR. If a reference an
array is passed then the first element is used in place of the \f(CW\*(C`#ifdef\*(C'\fR
line, and the second element in place of the \f(CW\*(C`#endif\*(C'\fR. This allows
pre-processor constructions such as
.Sp
.Vb 5
\&    #if defined (foo)
\&    #if !defined (bar)
\&    ...
\&    #endif
\&    #endif
.Ve
.Sp
to be used to determine if a constant is to be defined.
.Sp
A \*(L"macro\*(R" 1 signals that the constant is always defined, so the \f(CW\*(C`#if\*(C'\fR/\f(CW\*(C`#endif\*(C'\fR
test is omitted.
.IP "default" 8
.IX Item "default"
Default value to use (instead of \f(CW\*(C`croak\*(C'\fRing with \*(L"your vendor has not
defined...\*(R") to return if the macro isn't defined. Specify a reference to
an array with type followed by value(s).
.IP "pre" 8
.IX Item "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 \f(CW\*(C`struct\*(C'\fR
and return this as \fIvalue\fR. This C code is places at the start of a block,
so you can declare variables in it.
.IP "post" 8
.IX Item "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 \fIpre\fR.
Rarely needed.
.IP "def_pre" 8
.IX Item "def_pre"
.PD 0
.IP "def_post" 8
.IX Item "def_post"
.PD
Equivalents of \fIpre\fR and \fIpost\fR for the default value.
.IP "utf8" 8
.IX Item "utf8"
Generated internally. Is zero or undefined if name is 7 bit \s-1ASCII\s0,
\&\*(L"no\*(R" if the name is 8 bit (and so should only match if \fISvUTF8()\fR is false),
\&\*(L"yes\*(R" if the name is utf8 encoded.
.Sp
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.
.IP "weight" 8
.IX Item "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.
.RE
.RS 4
.Sp
In the argument hashref, \fIpackage\fR is the name of the package, and is only
used in comments inside the generated C code. \fIsubname\fR defaults to
\&\f(CW\*(C`constant\*(C'\fR if undefined.
.Sp
\&\fIdefault_type\fR is the type returned by \f(CW\*(C`ITEM\*(C'\fRs that don't specify their
type. It defaults to the value of \f(CW\*(C`default_type()\*(C'\fR. \fItypes\fR should be given
either as a comma separated list of types that the C subroutine \fIsubname\fR
will generate or as a reference to a hash. \fIdefault_type\fR will be added to
the list if not present, as will any types given in the list of \fI\s-1ITEM\s0\fRs. The
resultant list should be the same list of types that \f(CW\*(C`XS_constant\*(C'\fR is
given. [Otherwise \f(CW\*(C`XS_constant\*(C'\fR and \f(CW\*(C`C_constant\*(C'\fR may differ in the number of
parameters to the constant function. \fIindent\fR 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.
.Sp
\&\fIbreakout\fR governs when child functions of \fIsubname\fR are generated.  If there
are \fIbreakout\fR or more \fI\s-1ITEM\s0\fRs with the same length of name, then the code
to switch between them is placed into a function named \fIsubname\fR_\fIlen\fR, for
example \f(CW\*(C`constant_5\*(C'\fR for names 5 characters long.  The default \fIbreakout\fR is
3.  A single \f(CW\*(C`ITEM\*(C'\fR is always inlined.
.RE
.SH "BUGS"
.IX Header "BUGS"
Not everything is documented yet.
.PP
Probably others.
.SH "AUTHOR"
.IX Header "AUTHOR"
Nicholas Clark <[e-mail]> based on the code in \f(CW\*(C`h2xs\*(C'\fR by Larry Wall and
others