1enum(3) User Contributed Perl Documentation enum(3)
2
6 enum - C style enumerated types and bitmask flags in Perl
7
9 use enum qw(Sun Mon Tue Wed Thu Fri Sat);
10 # Sun == 0, Mon == 1, etc
11 use enum qw(Forty=40 FortyOne Five=5 Six Seven);
13 # Yes, you can change the start indexs at any time as in C
14 use enum qw(:Prefix_ One Two Three);
16 ## Creates Prefix_One, Prefix_Two, Prefix_Three
17 use enum qw(:Letters_ A..Z);
19 ## Creates Letters_A, Letters_B, Letters_C, ...
20 use enum qw(
22 :Months_=0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
23 :Days_=0 Sun Mon Tue Wed Thu Fri Sat
24 :Letters_=20 A..Z
25 );
26 ## Prefixes can be changed mid list and can have index changes too
27 use enum qw(BITMASK:LOCK_ SH EX NB UN);
29 ## Creates bitmask constants for LOCK_SH == 1, LOCK_EX == 2,
30 ## LOCK_NB == 4, and LOCK_UN == 8.
31 ## NOTE: This example is only valid on FreeBSD-2.2.5 however, so don't
32 ## actually do this. Import from Fnctl instead.
33
35 This module is used to define a set of constants with ordered numeric
36 values, similar to the "enum" type in the C programming language. You
37 can also define bitmask constants, where the value assigned to each
38 constant has exactly one bit set (eg 1, 2, 4, 8, etc).
39 What are enumerations good for? Typical uses would be for giving
41 mnemonic names to indexes of arrays. Such arrays might be a list of
42 months, days, or a return value index from a function such as
43 localtime():
44 use enum qw(
46 :Months_=0 Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
47 :Days_=0 Sun Mon Tue Wed Thu Fri Sat
48 :LC_=0 Sec Min Hour MDay Mon Year WDay YDay Isdst
49 );
50 if ((localtime)[LC_Mon] == Months_Jan) {
52 print "It's January!\n";
53 }
54 if ((localtime)[LC_WDay] == Days_Fri) {
55 print "It's Friday!\n";
56 }
57 This not only reads easier, but can also be typo-checked at compile
59 time when run under use strict. That is, if you misspell Days_Fri as
60 Days_Fry, you'll generate a compile error.
61
63 The BITMASK option allows the easy creation of bitmask constants such
64 as functions like flock() and sysopen() use. These are also very
65 useful for your own code as they allow you to efficiently store many
66 true/false options within a single integer.
67 use enum qw(BITMASK: MY_ FOO BAR CAT DOG);
69 my $foo = 0;
71 $foo |= MY_FOO;
72 $foo |= MY_DOG;
73 if ($foo & MY_DOG) {
75 print "foo has the MY_DOG option set\n";
76 }
77 if ($foo & (MY_BAR | MY_DOG)) {
78 print "foo has either the MY_BAR or MY_DOG option set\n"
79 }
80 $foo ^= MY_DOG; ## Turn MY_DOG option off (set its bit to false)
82 When using bitmasks, remember that you must use the bitwise operators,
84 |, &, ^, and ~. If you try to do an operation like "$foo += MY_DOG;"
85 and the MY_DOG bit has already been set, you'll end up setting other
86 bits you probably didn't want to set. You'll find the documentation
87 for these operators in the perlop manpage.
88 You can set a starting index for bitmasks just as you can for normal
90 enum values. But if the given index isn't a power of 2, then it won't
91 resolve to a single bit and therefore will generate a compile error.
92 Because of this, whenever you set the BITFIELD: directive, the index is
93 automatically set to 1. If you wish to go back to normal enum mode,
94 use the ENUM: directive. Similarly to the BITFIELD directive, the
95 ENUM: directive resets the index to 0. Here's an example:
96 use enum qw(
98 BITMASK:BITS_ FOO BAR CAT DOG
99 ENUM: FALSE TRUE
100 ENUM: NO YES
101 BITMASK: ONE TWO FOUR EIGHT SIX_TEEN
102 );
103 In this case, BITS_FOO, BITS_BAR, BITS_CAT, and BITS_DOG equal 1, 2, 4
105 and 8 respectively. FALSE and TRUE equal 0 and 1. NO and YES also
106 equal 0 and 1. And ONE, TWO, FOUR, EIGHT, and SIX_TEEN equal, you
107 guessed it, 1, 2, 4, 8, and 16.
108
110 Enum names can not be the same as method, function, or constant names.
111 This is probably a Good Thing[tm].
112 No way (that I know of) to cause compile time errors when one of these
114 enum names get redefined. IMHO, there is absolutely no time when
115 redefining a sub is a Good Thing[tm], and should be taken out of the
116 language, or at least have a pragma that can cause it to be a compile
117 time error.
118 Enumerated types are package scoped just like constants, not block
120 scoped as some other pragma modules are.
121 It supports A..Z nonsense. Can anyone give me a Real World[tm] reason
123 why anyone would ever use this feature...?
124
126 There are a number of modules that can be used to define enumerations:
127 Class::Enum, enum::fields, enum::hash, Readonly::Enum, Object::Enum,
128 Enumeration.
129 If you're using Moose, then MooseX::Enumeration may be of interest.
131 Type::Tiny::Enum is part of the Type-Tiny
132 <https://metacpan.org/release/Type-Tiny> distribution.
133 There are many CPAN modules related to defining constants in Perl; here
135 are some of the best ones: constant, Const::Fast, constant::lexical,
136 constant::our.
137 Neil Bowers has written a review of CPAN modules for definining
139 constants <http://neilb.org/reviews/constants.html>, which covers all
140 such modules.
141
143 <https://github.com/neilb/enum>
144
146 Originally written by Byron Brummer (ZENIN), now maintained by Neil
147 Bowers <neilb@cpan.org>.
148 Based on early versions of the constant module by Tom Phoenix.
150 Original implementation of an interface of Tom Phoenix's design by
152 Benjamin Holzman, for which we borrow the basic parse algorithm layout.
153
155 Copyright 1998 (c) Byron Brummer. Copyright 1998 (c) OMIX, Inc.
156 Permission to use, modify, and redistribute this module granted under
158 the same terms as Perl itself.
159perl v5.30.1 2020-01-30 enum(3)