enum - C style enumerated types and bitmask flags in Perl


enum - C style enumerated types and bitmask flags in Perl


  use enum qw(Sun Mon Tue Wed Thu Fri Sat);
  # Sun == 0, Mon == 1, etc
  use enum qw(Forty=40 FortyOne Five=5 Six Seven);
  # Yes, you can change the start indexs at any time as in C
  use enum qw(:Prefix_ One Two Three);
  ## Creates Prefix_One, Prefix_Two, Prefix_Three
  use enum qw(:Letters_ A..Z);
  ## Creates Letters_A, Letters_B, Letters_C, ...
  use enum qw(
      :Months_=0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
      :Days_=0   Sun Mon Tue Wed Thu Fri Sat
      :Letters_=20 A..Z
  ## Prefixes can be changed mid list and can have index changes too
  use enum qw(BITMASK:LOCK_ SH EX NB UN);
  ## Creates bitmask constants for LOCK_SH == 1, LOCK_EX == 2,
  ## LOCK_NB == 4, and LOCK_UN == 8.
  ## NOTE: This example is only valid on FreeBSD-2.2.5 however, so don't
  ## actually do this.  Import from Fnctl instead.


Defines a set of symbolic constants with ordered numeric values ala C enum types.

Now capable of creating creating ordered bitmask constants as well. See the BITMASKS section for details.

What are they good for? Typical uses would be for giving mnemonic names to indexes of arrays. Such arrays might be a list of months, days, or a return value index from a function such as localtime():

  use enum qw(
      :Months_=0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
      :Days_=0   Sun Mon Tue Wed Thu Fri Sat
      :LC_=0     Sec Min Hour MDay Mon Year WDay YDay Isdst
  if ((localtime)[LC_Mon] == Months_Jan) {
      print "It's January!\n";
  if ((localtime)[LC_WDay] == Days_Fri) {
      print "It's Friday!\n";

This not only reads easier, but can also be typo-checked at compile time when run under use strict. That is, if you misspell Days_Fri as Days_Fry, you'll generate a compile error.

BITMASKS, bitwise operations, and bitmask option values

The BITMASK option allows the easy creation of bitmask constants such as functions like flock() and sysopen() use. These are also very useful for your own code as they allow you to efficiently store many true/false options within a single integer.

    use enum qw(BITMASK: MY_ FOO BAR CAT DOG);
    my $foo = 0;
    $foo |= MY_FOO;
    $foo |= MY_DOG;

    if ($foo & MY_DOG) {
        print "foo has the MY_DOG option set\n";
    if ($foo & (MY_BAR | MY_DOG)) {
        print "foo has either the MY_BAR or MY_DOG option set\n"
    $foo ^= MY_DOG;  ## Turn MY_DOG option off (set its bit to false)

When using bitmasks, remember that you must use the bitwise operators, |, &, ^, and ~. If you try to do an operation like $foo += MY_DOG; and the MY_DOG bit has already been set, you'll end up setting other bits you probably didn't want to set. You'll find the documentation for these operators in the perlop manpage.

You can set a starting index for bitmasks just as you can for normal enum values, but if the given index isn't a power of 2 it won't resolve to a single bit and therefor will generate a compile error. Because of this, whenever you set the BITFIELD: directive, the index is automatically set to 1. If you wish to go back to normal enum mode, use the ENUM: directive. Similarly to the BITFIELD directive, the ENUM: directive resets the index to 0. Here's an example:

  use enum qw(
      ENUM: NO YES

In this case, BITS_FOO, BITS_BAR, BITS_CAT, and BITS_DOG equal 1, 2, 4 and 8 respectively. FALSE and TRUE equal 0 and 1. NO and YES also equal 0 and 1. And ONE, TWO, FOUR, EIGHT, and SIX_TEEN equal, you guessed it, 1, 2, 4, 8, and 16.


Enum names can not be the same as method, function, or constant names. This is probably a Good Thing[tm].

No way (that I know of) to cause compile time errors when one of these enum names get redefined. IMHO, there is absolutely no time when redefining a sub is a Good Thing[tm], and should be taken out of the language, or at least have a pragma that can cause it to be a compile time error.

Enumerated types are package scoped just like constants, not block scoped as some other pragma modules are.

It supports A..Z nonsense. Can anyone give me a Real World[tm] reason why anyone would ever use this feature...?


  $Log: enum.pm,v $
  Revision 1.16  1999/05/27 16:00:35  byron
  Fixed bug that caused bitwise operators to treat enum types as strings
  instead of numbers.
  Revision 1.15  1999/05/27 15:51:27  byron
  Add support for negative values.
  Added stricter hex value checks.
  Revision 1.14  1999/05/13 15:58:18  byron
  Fixed bug in hex index code that broke on 0xA.
  Revision 1.13  1999/05/13 10:52:30  byron
  Fixed auto-index bugs in new non-decimal numeric support.
  Revision 1.12  1999/05/13 10:00:45  byron
  Added support for non-decimal numeric representations ala 0x123, 0644, and
  First version committed to CVS.
  Revision 1.11  1998/07/18 17:53:05  byron
    -Added BITMASK and ENUM directives.
    -Revamped documentation.
  Revision 1.10  1998/06/12 20:12:50  byron
    -Removed test code
    -Released to CPAN
  Revision 1.9  1998/06/12 00:21:00  byron
    -Fixed -w warning when a null tag is used
  Revision 1.8  1998/06/11 23:04:53  byron
    -Fixed documentation bugs
    -Moved A..Z case to last as it's not going to be used
     as much as the other cases.
  Revision 1.7  1998/06/10 12:25:04  byron
    -Changed interface to match original design by Tom Phoenix
     as implemented in an early version of enum.pm by Benjamin Holzman.
    -Changed tag syntax to not require the 'PREFIX' string of Tom's
    -Allow multiple prefix tags to be used at any point.
    -Allowed index value changes from tags.
  Revision 1.6  1998/06/10 03:37:57  byron
    -Fixed superfulous -w warning
  Revision 1.4  1998/06/10 01:07:03  byron
    -Changed behaver to closer resemble C enum types
    -Changed docs to match new behaver


Zenin <zenin@archive.rhps.org>

aka Byron Brummer <byron@omix.com>.

Based off of the constant module by Tom Phoenix.

Original implementation of an interface of Tom Phoenix's design by Benjamin Holzman, for which we borrow the basic parse algorithm layout.


Copyright 1998 (c) Byron Brummer. Copyright 1998 (c) OMIX, Inc.

Permission to use, modify, and redistribute this module granted under the same terms as Perl.


constant(3), perl(1).

 enum - C style enumerated types and bitmask flags in Perl