Constant::Generate - Common tasks for symbolic constants
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');
"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.
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.
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.
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.
<
https://github.com/mnunberg/Constant-Generate>
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.