Provided by: libconstant-generate-perl_0.17-3_all 
NAME
Constant::Generate - Common tasks for symbolic constants
SYNOPSIS
Simplest use
use Constant::Generate [ qw(CONST_FOO CONST_BAR) ];
printf( "FOO=%d, BAR=%d\n", CONST_FOO, CONST_BAR );
Bitflags:
use Constant::Generate [qw(ANNOYING STRONG LAZY)], type => 'bits';
my $state = (ANNOYING|LAZY);
$state & STRONG == 0;
With reverse mapping:
use Constant::Generate
[qw(CLIENT_IRSSI CLIENT_XCHAT CLIENT_PURPLE)],
type => "bits",
mapname => "client_type_to_str";
my $client_type = CLIENT_IRSSI | CLIENT_PURPLE;
print client_type_to_str($client_type); #prints 'CLIENT_IRSSI|CLIENT_PURPLE';
Generate reverse maps, but do not generate values. also, push to exporter
#Must define @EXPORT_OK and tags beforehand
our @EXPORT_OK;
our %EXPORT_TAGS;
use Constant::Generate {
O_RDONLY => 00,
O_WRONLY => 01,
O_RDWR => 02,
O_CREAT => 0100
}, tag => "openflags", type => 'bits';
my $oflags = O_RDWR|O_CREAT;
print openflags_to_str($oflags); #prints 'O_RDWR|O_CREAT';
DWIM Constants
use Constant::Generate {
RDONLY => 00,
WRONLY => 01,
RDWR => 02,
CREAT => 0100
}, prefix => 'O_', dualvar => 1;
my $oflags = O_RDWR|O_CREAT;
O_RDWR eq 'RDWR';
Export to other packages
package My::Constants
BEGIN { $INC{'My/Constants.pm} = 1; }
use base qw(Exporter);
our (@EXPORT_OK,@EXPORT,%EXPORT_TAGS);
use Constant::Generate [qw(FOO BAR BAZ)],
tag => "my_constants",
export_ok => 1;
package My::User;
use My::Constants qw(:my_constants);
FOO == 0 && BAR == 1 && BAZ == 2 &&
my_constants_to_str(FOO eq 'FOO') && my_constants_to_str(BAR eq 'BAR') &&
my_constants_to_str(BAZ eq 'BAZ');
DESCRIPTION
"Constant::Generate" provides useful utilities for handling, debugging, and generating
opaque, 'magic-cookie' type constants as well as value-significant constants.
Using its simplest interface, it will generate a simple enumeration of names passed to it
on import.
Read import options to use.
USAGE
All options and configuration for this module are specified at import time.
The canonical usage of this module is
use Constant::Generate $symspec, %options;
Symbol Specifications
This is passed as the first argument to "import" and can exist as a reference to either a
hash or an array. In the case of an array reference, the array will just contain symbol
names whose values will be automatically assigned in order, with the first symbol being 0
and each subsequent symbol incrementing on the value of the previous. The default starting
value can be modified using the "start_at" option (see "Options").
If the symbol specification is a hashref, then keys are symbol names and values are the
symbol values, similar to what constant uses.
By default, symbols are assumed to correlate to a single independent integer value, and
any reverse mapping performed will only ever map a symbol value to a single symbol name.
For bitflags, it is possible to specify "type => 'bits'" in the "Options" which will
modify the auto-generation of the constants as well as provide suitable output for reverse
mapping functions.
Basic Options
The second argument to the import function is a hash of options.
All options may be prefixed by a dash ("-option") or in their 'bare' form ("option").
"type"
This specifies the type of constant used in the enumeration for the first argument as
well as the generation of reverse mapping functions. Valid values are ones matching
the regular expression "/bit/i" for bitfield values, and ones matching "/int/i" for
simple integer values.
You can also specify "/str/i" for string constants. When the symbol specification is
an array, the value for the string constants will be the strings themselves.
If "type" is not specified, it defaults to integer values.
"start_at"
Only valid for auto-generated numeric values. This specifies the starting value for
the first constant of the enumeration. If the enumeration is a bitfield, then the
value is a factor by which to left-shift 1, thus
use Constant::Generate [qw(OPT_FOO OPT_BAR)], type => "bits";
OPT_FOO == 1 << 0;
OPT_BAR == 1 << 1;
#are true
and so on.
For non-bitfield values, this is simply a counter:
use Constant::Generate [qw(CONST_FOO CONST_BAR)], start_at => 42;
CONST_FOO == 42;
CONST_BAR == 43;
"tag"
Specify a tag to use for the enumeration.
This tag is used to generate the reverse mapping function, and is also the key under
which symbols will be exported via %EXPORT_TAGS.
"mapname"
Specify the name of the reverse mapping function for the enumeration. If this is
omitted, it will default to the form
$tag . "_to_str";
where $tag is the "tag" option passed. If neither are specified, then a reverse
mapping function will not be generated.
"export", "export_ok", "export_tags"
This group of options specifies the usage and modification of @EXPORT, @EXPORT_OK and
%EXPORT_TAGS respectively, which are used by Exporter.
Values for these options should either be simple scalar booleans, or reference objects
corresponding to the appropriate variables.
If references are not used as values for these options, "Constant::Generate" will
expect you to have defined these modules already, and otherwise die.
"prefix"
Set this to a string to be prefixed to all constant names declared in the symbol
specification; thus the following are equivalent:
use Constant::Generate [qw( MY_FOO MY_BAR MY_BAZ )];
With auto-prefixing:
use Constant::Generate [qw( FOO BAR BAZ )], prefix => "MY_";
"show_prefix"
When prefixes are specified, the default is that reverse mapping functions will
display only the 'bare', user-specified name. Thus:
use Constant::Generate [qw( FOO )], prefix => "MY_", mapname => "const_str";
const_str(MY_FOO) eq 'FOO';
Setting "show_prefix" to a true value will display the full name.
Dual-Var Constants
Use of dual variable constants (which return an integer or string value depending on the
context) can be enabled by passing "stringy_vars" to "Constant::Generate", or using
"Constant::Generate::Dualvar":
"stringy_vars"
"dualvar"
This will apply some trickery to the values returned by the constant symbols.
Normally, constant symbols will return only their numeric value, and a reverse mapping
function is needed to retrieve the original symbolic name.
When "dualvar" is set to a true value the values returned by the constant subroutine
will do the right thing in string and numeric contexts; thus:
use Constant::Generate::Dualvar [qw(FOO BAR)];
FOO eq 'FOO';
FOO == 0;
The "show_prefix" option controls whether the prefix is part of the stringified form.
Do not rely too much on "dualvar" to magically convert any number into some meaningful
string form. In particular, it will only work on scalars which are directly descended
from the constant symbols. Paritcularly, this means that unpack()ing or receiving data
from a different process will not result in these special stringy variables.
The "stringy_vars" option is an alias for "dualvar", which is supported for backwards
compatibility.
Listings
The following options enable constant subroutines which return lists of the symbols or
their values:
use Constant::Generate [qw(
FOO BAR BAZ
)],
allvalues => "VALS",
allsyms => "SYMS";
printf "VALUES: %s\n", join(", ", VALUES);
# => 0, 1, 2 (in no particular order)
printf "SYMBOLS: %s\n", join(", ", SYMS);
# => FOO, BAR, BAZ (in no particular order)
Or something potentially more useful:
use Constant::Generate [qw(
COUGH
SNEEZE
HICCUP
ZOMBIES
)],
type => 'bits',
allvalues => 'symptoms',
mapname => "symptom_str";
my $remedies = {
COUGH, "Take some honey",
SNEEZE, "Buy some tissues",
HICCUP, "Drink some water"
};
my $patient = SNEEZE | COUGH | ZOMBIES;
foreach my $symptom (symptoms()) {
next unless $patient & $symptom;
my $remedy = $remedies->{$symptom};
if(!$remedy) {
printf "Uh-Oh, we don't have a remedy for %s. Go to a hospital!\n",
symptom_str($symptom);
} else {
printf "You should: %s\n", $remedy;
}
}
"allvalues"
Sometimes it is convenient to have a list of all the constants defined in the
enumeration. Setting "allvalues" will make "Constant::Generate" create a like-named
constant subroutine which will return a list of all the values created.
"allsyms"
Like "allvalues", but will return a list of strings for the constants in the
enumeration.
EXPORTING
This module also allows you to define a 'constants' module of your own, from which you can
export constants to other files in your package. Figuring out the right exporter
parameters is quite hairy, and the export options can natually be a bit tricky.
In order to successfully export symbols made by this module, you must specify either
"export_ok" or "export" as hash options to "import". These correspond to the like-named
variables documented by Exporter.
Additionally, export tags can be specified only if one of the "export" flags is set to
true (again, following the behavior of "Exporter"). The auto-export feature is merely one
of syntactical convenience, but these three forms are effectively equivalent:
Nicest way:
use base qw(Exporter);
our (@EXPORT, %EXPORT_TAGS);
use Constant::Generate
[qw(FOO BAR BAZ)],
export => 1,
tag => "some_constants"
;
A bit more explicit:
use base qw(Exporter);
use Constant::Generate
[qw(FOO BAR BAZ)],
export => \our @EXPORT,
export_tags => \our %EXPORT_TAGS,
tag => "some_constants",
mapname => "some_constants_to_str",
;
Or DIY:
use base qw(Exporter);
our @EXPORT;
my @SYMS;
BEGIN {
@SYMS = qw(FOO BAR BAZ);
}
use Constant::Generate \@SYMS, mapname => "some_constants_to_str";
push @EXPORT, @SYMS, "some_constants_to_str";
$EXPORT_TAGS{'some_constants'} = [@SYMS, "some_constants_to_str"];
Also note that any "allvalues", "allsyms", or "mapname" subroutines will be exported
according to whatever specifications were configured for the constants themselves.
NOTES
The "dualvar" or "stringy_var" option can be short-handed by doing the following:
use Constant::Generate::Dualvar [qw(
FOO
BAR
BAZ
)], prefix => 'MY_';
MY_FOO eq 'FOO';
etc.
BUGS & TODO
It's somewhat ironic that a module which aims to promote the use of symbolic constants has
all of its configuration options determined by hashes and strings.
REPOSITORY
<https://github.com/mnunberg/Constant-Generate>
AUTHOR & COPYRIGHT
Copyright (c) 2011 by M. Nunberg
You may use and distribute this software under the same terms and conditions as Perl
itself, OR under the terms and conditions of the GNU GPL, version 2 or greater.