How to implement Enums in Ruby

Question

What s the best way to implement the enum idiom in Ruby  I m looking for something which I can use  almost  like the Java C  enums

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This is my approach to enums in Ruby  I was going for short and sweet  not necessarily the the most C-like  Any thoughts  module Kernel   def enum values      Module new do  mod        values each with index   v i  mod const set v to s capitalize  2  i           def mod inspect          quot   self name     self constants join         quot        end     end   end end  States   enum  w Draft Published Trashed    gt  States  Draft  Published  Trashed    States  Draft   gt  1  States  Published   gt  2  States  Trashed   gt  4  States  Draft   States  Trashed   gt  5

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Another way to mimic an enum with consistent equality handling  shamelessly adopted from Dave Thomas   Allows open enums  much like symbols  and closed  predefined  enums   class Enum   def self new values   nil      enum   Class new do       unless values         def self const missing name            const set name  new name           end       end        def initialize name           enum name   name       end        def to s            self class     enum name        end     end      if values       enum instance eval do         values each    e  const set e  enum new e           end     end      enum   end end  Genre   Enum new  w Gothic Metal    creates closed enum Architecture   Enum new             creates open enum  Genre  Gothic    Genre  Gothic            gt  true Genre  Gothic    Architecture  Gothic     gt  true

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Try the inum  https   github com alfa-jpn inum  class Color  lt  Inum  Base   define  RED   define  GREEN   define  BLUE end   Color  RED  Color parse  blue       gt  Color  BLUE Color parse 2           gt  Color  GREEN   see more https   github com alfa-jpn inum usage

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It all depends how you use Java or C  enums  How you use it will dictate the solution you ll choose in Ruby   Try the native Set type  for instance    gt  gt  enum   Set  a    b    c     gt    lt Set    a    b    c   gt   gt  gt  enum member   b    gt  true  gt  gt  enum member   d    gt  false  gt  gt  enum add   b    gt  nil  gt  gt  enum add   d    gt    lt Set    a    b    c    d   gt

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Symbols is the ruby way  However  sometimes one need to talk to some C code or something or Java that expose some enum for various things      server roles rb module EnumLike    def EnumLike server role     server Symb    SERVER CLOUD   SERVER DESKTOP   SERVER WORKSTATION      server Enum Hash new     i 0     server Symb each   e  server Enum e  i  i   1      return server Symb server Enum   end  end     This can then be used like this    require  server roles   sSymb  sEnum  EnumLike server role    foreignvec sEnum  SERVER WORKSTATION   8     This is can of course be made abstract and you can roll our own Enum class

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I use the following approach   class MyClass   MY ENUM    MY VALUE 1    value1   MY VALUE 2    value2   end   I like it for the following advantages    It groups values visually as one whole It does some compilation-time checking  in contrast with just using symbols  I can easily access the list of all possible values  just MY ENUM I can easily access distinct values  MY VALUE 1 It can have values of any type  not just Symbol   Symbols may be better cause you don t have to write the name of outer class  if you are using it in another class  MyClass  MY VALUE 1

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I use the following approach   class MyClass   MY ENUM    MY VALUE 1    value1   MY VALUE 2    value2   end   I like it for the following advantages    It groups values visually as one whole It does some compilation-time checking  in contrast with just using symbols  I can easily access the list of all possible values  just MY ENUM I can easily access distinct values  MY VALUE 1 It can have values of any type  not just Symbol   Symbols may be better cause you don t have to write the name of outer class  if you are using it in another class  MyClass  MY VALUE 1

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Most people use symbols  that s the  foo bar syntax   They re sort of unique opaque values  Symbols don t belong to any enum-style type so they re not really a faithful representation of C s enum type but this is pretty much as good as it gets

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I have implemented enums like that   module EnumType    def self find by id id     if id instance of  String       id   id to i     end      values each do  type        if id    type id         return type       end     end     nil   end    def self values       ENUM 1   ENUM 2     end    class Enum     attr reader  id   label      def initialize id  label        id   id        label   label     end   end     ENUM 1   Enum new 1   first      ENUM 2   Enum new 2   second    end   then its easy to do operations   EnumType ENUM 1 label        enum   EnumType find by id 1        valueArray   EnumType values

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irb main  016 0 gt  num  1 2 3 4  irb main  017 0 gt  alph   a   b   c   d   irb main  018 0 gt  l enum alph to enum irb main  019 0 gt  s enum num to enum irb main  020 0 gt  loop do irb main  021 1  puts    s enum next  -   l enum next   irb main  022 1 gt  end   Output   1 - a 2 - b 3 - c 4 - d

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Perhaps the best lightweight approach would be  module MyConstants   ABC   Class new   DEF   Class new   GHI   Class new end   This way values have associated names  as in Java C    MyConstants  ABC   gt  MyConstants  ABC   To get all values  you can do  MyConstants constants   gt    ABC   DEF   GHI     If you want an enum s ordinal value  you can do  MyConstants constants index  GHI   gt  2

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Two ways  Symbols   foo notation  or constants  FOO notation   Symbols are appropriate when you want to enhance readability without littering code with literal strings  postal code  minnesota     quot MN quot  postal code  new york     quot NY quot   Constants are appropriate when you have an underlying value that is important  Just declare a module to hold your constants and then declare the constants within that  module Foo   BAR   1   BAZ   2   BIZ   4 end   flags   Foo  BAR   Foo  BAZ   flags   3  Added 2021-01-17 If you are passing the enum value around  for example  storing it in a database  and you need to be able to translate the value back into the symbol  there s a mashup of both approaches COMMODITY TYPE       currency  1    investment  2     def commodity type string value    COMMODITY TYPE key value  end  COMMODITY TYPE  currency   This approach inspired by andrew-grimm s answer https   stackoverflow com a 5332950 13468 I d also recommend reading through the rest of the answers here since there are a lot of ways to solve this and it really boils down to what it is about the other language s enum that you care about

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I think the best way to implement enumeration like types is with symbols since the pretty much behave as integer  when it comes to performace  object id is used to make comparisons     you don t need to worry about indexing and they look really neat in your code xD

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Another solution is using OpenStruct  Its pretty straight forward and clean   https   ruby-doc org stdlib-2 3 1 libdoc ostruct rdoc OpenStruct html  Example     bar rb require  ostruct    not needed when using Rails    by patching Array you have a simple way of creating a ENUM-style class Array    def to enum base 0        OpenStruct new map with index base  to h     end end  class Bar      MY ENUM   OpenStruct new ONE  1  TWO  2  THREE  3      MY ENUM2    w ONE TWO THREE  to enum      def use enum  value          case value         when MY ENUM ONE             puts  Hello  this is ENUM 1          when MY ENUM TWO             puts  Hello  this is ENUM 2          when MY ENUM THREE             puts  Hello  this is ENUM 3          else             puts    value  not found in ENUM          end     end  end    usage foo   Bar new     foo use enum 1 foo use enum 2 foo use enum 9     put this code in a file  bar rb   start IRB and type  load  bar rb

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The most idiomatic way to do this is to use symbols   For example  instead of   enum     FOO    BAR    BAZ    myFunc FOO        you can just use symbols     You don t actually need to declare these  of course--this is   just to show you what symbols look like   foo  bar  baz  my func  foo    This is a bit more open-ended than enums  but it fits well with the Ruby spirit   Symbols also perform very well  Comparing two symbols for equality  for example  is much faster than comparing two strings

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Symbols is the ruby way  However  sometimes one need to talk to some C code or something or Java that expose some enum for various things      server roles rb module EnumLike    def EnumLike server role     server Symb    SERVER CLOUD   SERVER DESKTOP   SERVER WORKSTATION      server Enum Hash new     i 0     server Symb each   e  server Enum e  i  i   1      return server Symb server Enum   end  end     This can then be used like this    require  server roles   sSymb  sEnum  EnumLike server role    foreignvec sEnum  SERVER WORKSTATION   8     This is can of course be made abstract and you can roll our own Enum class

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I m surprised that no one has offered something like the following  harvested from the RAPI gem    class Enum    private    def self enum attr name  num      name   name to s      define method name        do        attrs  amp  num    0     end      define method name        do  set        if set          attrs    num       else          attrs  amp    num       end     end   end    public    def initialize attrs   0       attrs   attrs   end    def to i      attrs   end end   Which can be used like so   class FileAttributes  lt  Enum   enum attr  readonly        0x0001   enum attr  hidden          0x0002   enum attr  system          0x0004   enum attr  directory       0x0010   enum attr  archive         0x0020   enum attr  in rom          0x0040   enum attr  normal          0x0080   enum attr  temporary       0x0100   enum attr  sparse          0x0200   enum attr  reparse point   0x0400   enum attr  compressed      0x0800   enum attr  rom module      0x2000 end   Example    gt  gt  example   FileAttributes new 3    gt    lt FileAttributes 0x629d90  attrs 3 gt   gt  gt  example readonly    gt  true  gt  gt  example hidden    gt  true  gt  gt  example system    gt  false  gt  gt  example system   true   gt  true  gt  gt  example system    gt  true  gt  gt  example to i   gt  7   This plays well in database scenarios  or when dealing with C style constants enums  as is the case when using FFI  which RAPI makes extensive use of    Also  you don t have to worry about typos causing silent failures  as you would with using a hash-type solution

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If you are using Rails 4 2 or greater you can use Rails enums   Rails now has enums by default without the need for including any gems   This is very similar  and more with features  to Java  C   enums   Quoted from http   edgeapi rubyonrails org classes ActiveRecord Enum html    class Conversation  lt  ActiveRecord  Base   enum status     active   archived   end    conversation update  status  0 conversation active  conversation active      gt  true conversation status      gt   active     conversation update  status  1 conversation archived  conversation archived      gt  true conversation status        gt   archived     conversation update  status  1 conversation status    archived     conversation update  status  nil conversation status   nil conversation status nil      gt  true conversation status          gt  nil

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This is my approach to enums in Ruby  I was going for short and sweet  not necessarily the the most C-like  Any thoughts  module Kernel   def enum values      Module new do  mod        values each with index   v i  mod const set v to s capitalize  2  i           def mod inspect          quot   self name     self constants join         quot        end     end   end end  States   enum  w Draft Published Trashed    gt  States  Draft  Published  Trashed    States  Draft   gt  1  States  Published   gt  2  States  Trashed   gt  4  States  Draft   States  Trashed   gt  5

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This seems a bit superfluous  but this is a methodology that I have used a few times  especially where I am integrating with xml or some such    model class Profession   def self pro enum       BAKER   gt  0         MANAGER   gt  1         FIREMAN   gt  2         DEV   gt  3         VAL   gt    BAKER    MANAGER    FIREMAN    DEV           end end  Profession pro enum  DEV          gt 3 Profession pro enum  VAL  1       gt MANAGER   This gives me the rigor of a c  enum and it is tied to the model

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Most people use symbols  that s the  foo bar syntax   They re sort of unique opaque values  Symbols don t belong to any enum-style type so they re not really a faithful representation of C s enum type but this is pretty much as good as it gets

User · Answer

Another way to mimic an enum with consistent equality handling  shamelessly adopted from Dave Thomas   Allows open enums  much like symbols  and closed  predefined  enums   class Enum   def self new values   nil      enum   Class new do       unless values         def self const missing name            const set name  new name           end       end        def initialize name           enum name   name       end        def to s            self class     enum name        end     end      if values       enum instance eval do         values each    e  const set e  enum new e           end     end      enum   end end  Genre   Enum new  w Gothic Metal    creates closed enum Architecture   Enum new             creates open enum  Genre  Gothic    Genre  Gothic            gt  true Genre  Gothic    Architecture  Gothic     gt  true

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This seems a bit superfluous  but this is a methodology that I have used a few times  especially where I am integrating with xml or some such    model class Profession   def self pro enum       BAKER   gt  0         MANAGER   gt  1         FIREMAN   gt  2         DEV   gt  3         VAL   gt    BAKER    MANAGER    FIREMAN    DEV           end end  Profession pro enum  DEV          gt 3 Profession pro enum  VAL  1       gt MANAGER   This gives me the rigor of a c  enum and it is tied to the model

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Two ways  Symbols   foo notation  or constants  FOO notation   Symbols are appropriate when you want to enhance readability without littering code with literal strings  postal code  minnesota     quot MN quot  postal code  new york     quot NY quot   Constants are appropriate when you have an underlying value that is important  Just declare a module to hold your constants and then declare the constants within that  module Foo   BAR   1   BAZ   2   BIZ   4 end   flags   Foo  BAR   Foo  BAZ   flags   3  Added 2021-01-17 If you are passing the enum value around  for example  storing it in a database  and you need to be able to translate the value back into the symbol  there s a mashup of both approaches COMMODITY TYPE       currency  1    investment  2     def commodity type string value    COMMODITY TYPE key value  end  COMMODITY TYPE  currency   This approach inspired by andrew-grimm s answer https   stackoverflow com a 5332950 13468 I d also recommend reading through the rest of the answers here since there are a lot of ways to solve this and it really boils down to what it is about the other language s enum that you care about

User · Answer

Two ways  Symbols   foo notation  or constants  FOO notation   Symbols are appropriate when you want to enhance readability without littering code with literal strings  postal code  minnesota     quot MN quot  postal code  new york     quot NY quot   Constants are appropriate when you have an underlying value that is important  Just declare a module to hold your constants and then declare the constants within that  module Foo   BAR   1   BAZ   2   BIZ   4 end   flags   Foo  BAR   Foo  BAZ   flags   3  Added 2021-01-17 If you are passing the enum value around  for example  storing it in a database  and you need to be able to translate the value back into the symbol  there s a mashup of both approaches COMMODITY TYPE       currency  1    investment  2     def commodity type string value    COMMODITY TYPE key value  end  COMMODITY TYPE  currency   This approach inspired by andrew-grimm s answer https   stackoverflow com a 5332950 13468 I d also recommend reading through the rest of the answers here since there are a lot of ways to solve this and it really boils down to what it is about the other language s enum that you care about

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I know it s been a long time since the guy posted this question  but I had the same question and this post didn t give me the answer  I wanted an easy way to see what the number represents  easy comparison  and most of all ActiveRecord support for lookup using the column representing the enum   I didn t find anything  so I made an awesome implementation called yinum which allowed everything I was looking for  Made ton of specs  so I m pretty sure it s safe   Some example features   COLORS   Enum new  COLORS   red   gt  1   green   gt  2   blue   gt  3    gt  COLORS  red   gt  1   green   gt  2   blue   gt  3  COLORS red    1  amp  amp  COLORS red     red   gt  true  class Car  lt  ActiveRecord  Base       attr enum  color   COLORS   red   gt  1   black   gt  2 end car   Car new car color    red    red    1    1  car color   gt  Car  COLORS red car color black    gt  false Car red to sql   gt   SELECT  cars    FROM  cars  WHERE  cars   color    1  Car last red    gt  true

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Two ways  Symbols   foo notation  or constants  FOO notation   Symbols are appropriate when you want to enhance readability without littering code with literal strings  postal code  minnesota     quot MN quot  postal code  new york     quot NY quot   Constants are appropriate when you have an underlying value that is important  Just declare a module to hold your constants and then declare the constants within that  module Foo   BAR   1   BAZ   2   BIZ   4 end   flags   Foo  BAR   Foo  BAZ   flags   3  Added 2021-01-17 If you are passing the enum value around  for example  storing it in a database  and you need to be able to translate the value back into the symbol  there s a mashup of both approaches COMMODITY TYPE       currency  1    investment  2     def commodity type string value    COMMODITY TYPE key value  end  COMMODITY TYPE  currency   This approach inspired by andrew-grimm s answer https   stackoverflow com a 5332950 13468 I d also recommend reading through the rest of the answers here since there are a lot of ways to solve this and it really boils down to what it is about the other language s enum that you care about

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Someone went ahead and wrote a ruby gem called Renum  It claims to get the closest Java C  like behavior  Personally I m still learning Ruby  and I was a little shocked when I wanted to make a specific class contain a static enum  possibly a hash  that it wasn t exactly easily found via google

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Recently we released a gem that implements Enums in Ruby  In my post you will find the answers on your questions  Also I described there why our implementation is better than existing ones  actually there are many implementations of this feature in Ruby yet as gems

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Another approach is to use a Ruby class with a hash containing names and values as described in the following RubyFleebie blog post  This allows you to convert easily between values and constants  especially if you add a class method to lookup the name for a given value

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The most idiomatic way to do this is to use symbols   For example  instead of   enum     FOO    BAR    BAZ    myFunc FOO        you can just use symbols     You don t actually need to declare these  of course--this is   just to show you what symbols look like   foo  bar  baz  my func  foo    This is a bit more open-ended than enums  but it fits well with the Ruby spirit   Symbols also perform very well  Comparing two symbols for equality  for example  is much faster than comparing two strings

User · Answer

It all depends how you use Java or C  enums  How you use it will dictate the solution you ll choose in Ruby   Try the native Set type  for instance    gt  gt  enum   Set  a    b    c     gt    lt Set    a    b    c   gt   gt  gt  enum member   b    gt  true  gt  gt  enum member   d    gt  false  gt  gt  enum add   b    gt  nil  gt  gt  enum add   d    gt    lt Set    a    b    c    d   gt

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If you re worried about typos with symbols  make sure your code raises an exception when you access a value with a non-existent key  You can do this by using fetch rather than      my value   my hash fetch  key    or by making the hash raise an exception by default if you supply a non-existent key   my hash   Hash new do  hash  key    raise  You tried to access using   key inspect  when the only keys we have are   hash keys inspect   end   If the hash already exists  you can add on exception-raising behaviour   my hash   Hash   1 2    my hash default proc   proc do  hash  key    raise  You tried to access using   key inspect  when the only keys we have are   hash keys inspect   end   Normally  you don t have to worry about typo safety with constants  If you misspell a constant name  it ll usually raise an exception

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Another approach is to use a Ruby class with a hash containing names and values as described in the following RubyFleebie blog post  This allows you to convert easily between values and constants  especially if you add a class method to lookup the name for a given value

User · Answer

It all depends how you use Java or C  enums  How you use it will dictate the solution you ll choose in Ruby   Try the native Set type  for instance    gt  gt  enum   Set  a    b    c     gt    lt Set    a    b    c   gt   gt  gt  enum member   b    gt  true  gt  gt  enum member   d    gt  false  gt  gt  enum add   b    gt  nil  gt  gt  enum add   d    gt    lt Set    a    b    c    d   gt

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I think the best way to implement enumeration like types is with symbols since the pretty much behave as integer  when it comes to performace  object id is used to make comparisons     you don t need to worry about indexing and they look really neat in your code xD

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I m surprised that no one has offered something like the following  harvested from the RAPI gem    class Enum    private    def self enum attr name  num      name   name to s      define method name        do        attrs  amp  num    0     end      define method name        do  set        if set          attrs    num       else          attrs  amp    num       end     end   end    public    def initialize attrs   0       attrs   attrs   end    def to i      attrs   end end   Which can be used like so   class FileAttributes  lt  Enum   enum attr  readonly        0x0001   enum attr  hidden          0x0002   enum attr  system          0x0004   enum attr  directory       0x0010   enum attr  archive         0x0020   enum attr  in rom          0x0040   enum attr  normal          0x0080   enum attr  temporary       0x0100   enum attr  sparse          0x0200   enum attr  reparse point   0x0400   enum attr  compressed      0x0800   enum attr  rom module      0x2000 end   Example    gt  gt  example   FileAttributes new 3    gt    lt FileAttributes 0x629d90  attrs 3 gt   gt  gt  example readonly    gt  true  gt  gt  example hidden    gt  true  gt  gt  example system    gt  false  gt  gt  example system   true   gt  true  gt  gt  example system    gt  true  gt  gt  example to i   gt  7   This plays well in database scenarios  or when dealing with C style constants enums  as is the case when using FFI  which RAPI makes extensive use of    Also  you don t have to worry about typos causing silent failures  as you would with using a hash-type solution

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Check out the ruby-enum gem  https   github com dblock ruby-enum   class Gender   include Enum    Gender define  MALE   male    Gender define  FEMALE   female  end  Gender all Gender  MALE

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Sometimes all I need is to be able to fetch enum s value and identify its name similar to java world   module Enum      def get value str         const get str       end      def get name sym         sym to s upcase      end  end   class Fruits    include Enum    APPLE    Delicious     MANGO    Sweet   end   Fruits get value  APPLE     Delicious   Fruits get value  MANGO      Sweet    Fruits get name  apple     APPLE   Fruits get name  mango     MANGO    This to me serves the purpose of enum and keeps it very extensible too  You can add more methods to the Enum class and viola get them for free in all the defined enums  for example  get all names and stuff like that

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module Status   BAD    13   GOOD   24    def self to str status      for sym in self constants       if self const get sym     status         return sym to s       end     end   end  end   mystatus   Status  GOOD  puts Status  to str mystatus    Output   GOOD

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Check out the ruby-enum gem  https   github com dblock ruby-enum   class Gender   include Enum    Gender define  MALE   male    Gender define  FEMALE   female  end  Gender all Gender  MALE

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Recently we released a gem that implements Enums in Ruby  In my post you will find the answers on your questions  Also I described there why our implementation is better than existing ones  actually there are many implementations of this feature in Ruby yet as gems

User · Answer

It all depends how you use Java or C  enums  How you use it will dictate the solution you ll choose in Ruby   Try the native Set type  for instance    gt  gt  enum   Set  a    b    c     gt    lt Set    a    b    c   gt   gt  gt  enum member   b    gt  true  gt  gt  enum member   d    gt  false  gt  gt  enum add   b    gt  nil  gt  gt  enum add   d    gt    lt Set    a    b    c    d   gt

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The most idiomatic way to do this is to use symbols   For example  instead of   enum     FOO    BAR    BAZ    myFunc FOO        you can just use symbols     You don t actually need to declare these  of course--this is   just to show you what symbols look like   foo  bar  baz  my func  foo    This is a bit more open-ended than enums  but it fits well with the Ruby spirit   Symbols also perform very well  Comparing two symbols for equality  for example  is much faster than comparing two strings

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Another solution is using OpenStruct  Its pretty straight forward and clean   https   ruby-doc org stdlib-2 3 1 libdoc ostruct rdoc OpenStruct html  Example     bar rb require  ostruct    not needed when using Rails    by patching Array you have a simple way of creating a ENUM-style class Array    def to enum base 0        OpenStruct new map with index base  to h     end end  class Bar      MY ENUM   OpenStruct new ONE  1  TWO  2  THREE  3      MY ENUM2    w ONE TWO THREE  to enum      def use enum  value          case value         when MY ENUM ONE             puts  Hello  this is ENUM 1          when MY ENUM TWO             puts  Hello  this is ENUM 2          when MY ENUM THREE             puts  Hello  this is ENUM 3          else             puts    value  not found in ENUM          end     end  end    usage foo   Bar new     foo use enum 1 foo use enum 2 foo use enum 9     put this code in a file  bar rb   start IRB and type  load  bar rb

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Most people use symbols  that s the  foo bar syntax   They re sort of unique opaque values  Symbols don t belong to any enum-style type so they re not really a faithful representation of C s enum type but this is pretty much as good as it gets

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Perhaps the best lightweight approach would be  module MyConstants   ABC   Class new   DEF   Class new   GHI   Class new end   This way values have associated names  as in Java C    MyConstants  ABC   gt  MyConstants  ABC   To get all values  you can do  MyConstants constants   gt    ABC   DEF   GHI     If you want an enum s ordinal value  you can do  MyConstants constants index  GHI   gt  2

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If you are using Rails 4 2 or greater you can use Rails enums   Rails now has enums by default without the need for including any gems   This is very similar  and more with features  to Java  C   enums   Quoted from http   edgeapi rubyonrails org classes ActiveRecord Enum html    class Conversation  lt  ActiveRecord  Base   enum status     active   archived   end    conversation update  status  0 conversation active  conversation active      gt  true conversation status      gt   active     conversation update  status  1 conversation archived  conversation archived      gt  true conversation status        gt   archived     conversation update  status  1 conversation status    archived     conversation update  status  nil conversation status   nil conversation status nil      gt  true conversation status          gt  nil

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Try the inum  https   github com alfa-jpn inum  class Color  lt  Inum  Base   define  RED   define  GREEN   define  BLUE end   Color  RED  Color parse  blue       gt  Color  BLUE Color parse 2           gt  Color  GREEN   see more https   github com alfa-jpn inum usage

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Sometimes all I need is to be able to fetch enum s value and identify its name similar to java world   module Enum      def get value str         const get str       end      def get name sym         sym to s upcase      end  end   class Fruits    include Enum    APPLE    Delicious     MANGO    Sweet   end   Fruits get value  APPLE     Delicious   Fruits get value  MANGO      Sweet    Fruits get name  apple     APPLE   Fruits get name  mango     MANGO    This to me serves the purpose of enum and keeps it very extensible too  You can add more methods to the Enum class and viola get them for free in all the defined enums  for example  get all names and stuff like that

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irb main  016 0 gt  num  1 2 3 4  irb main  017 0 gt  alph   a   b   c   d   irb main  018 0 gt  l enum alph to enum irb main  019 0 gt  s enum num to enum irb main  020 0 gt  loop do irb main  021 1  puts    s enum next  -   l enum next   irb main  022 1 gt  end   Output   1 - a 2 - b 3 - c 4 - d

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I know it s been a long time since the guy posted this question  but I had the same question and this post didn t give me the answer  I wanted an easy way to see what the number represents  easy comparison  and most of all ActiveRecord support for lookup using the column representing the enum   I didn t find anything  so I made an awesome implementation called yinum which allowed everything I was looking for  Made ton of specs  so I m pretty sure it s safe   Some example features   COLORS   Enum new  COLORS   red   gt  1   green   gt  2   blue   gt  3    gt  COLORS  red   gt  1   green   gt  2   blue   gt  3  COLORS red    1  amp  amp  COLORS red     red   gt  true  class Car  lt  ActiveRecord  Base       attr enum  color   COLORS   red   gt  1   black   gt  2 end car   Car new car color    red    red    1    1  car color   gt  Car  COLORS red car color black    gt  false Car red to sql   gt   SELECT  cars    FROM  cars  WHERE  cars   color    1  Car last red    gt  true

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If you re worried about typos with symbols  make sure your code raises an exception when you access a value with a non-existent key  You can do this by using fetch rather than      my value   my hash fetch  key    or by making the hash raise an exception by default if you supply a non-existent key   my hash   Hash new do  hash  key    raise  You tried to access using   key inspect  when the only keys we have are   hash keys inspect   end   If the hash already exists  you can add on exception-raising behaviour   my hash   Hash   1 2    my hash default proc   proc do  hash  key    raise  You tried to access using   key inspect  when the only keys we have are   hash keys inspect   end   Normally  you don t have to worry about typo safety with constants  If you misspell a constant name  it ll usually raise an exception

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Most people use symbols  that s the  foo bar syntax   They re sort of unique opaque values  Symbols don t belong to any enum-style type so they re not really a faithful representation of C s enum type but this is pretty much as good as it gets

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Someone went ahead and wrote a ruby gem called Renum  It claims to get the closest Java C  like behavior  Personally I m still learning Ruby  and I was a little shocked when I wanted to make a specific class contain a static enum  possibly a hash  that it wasn t exactly easily found via google

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module Status   BAD    13   GOOD   24    def self to str status      for sym in self constants       if self const get sym     status         return sym to s       end     end   end  end   mystatus   Status  GOOD  puts Status  to str mystatus    Output   GOOD

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The most idiomatic way to do this is to use symbols   For example  instead of   enum     FOO    BAR    BAZ    myFunc FOO        you can just use symbols     You don t actually need to declare these  of course--this is   just to show you what symbols look like   foo  bar  baz  my func  foo    This is a bit more open-ended than enums  but it fits well with the Ruby spirit   Symbols also perform very well  Comparing two symbols for equality  for example  is much faster than comparing two strings

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I have implemented enums like that   module EnumType    def self find by id id     if id instance of  String       id   id to i     end      values each do  type        if id    type id         return type       end     end     nil   end    def self values       ENUM 1   ENUM 2     end    class Enum     attr reader  id   label      def initialize id  label        id   id        label   label     end   end     ENUM 1   Enum new 1   first      ENUM 2   Enum new 2   second    end   then its easy to do operations   EnumType ENUM 1 label        enum   EnumType find by id 1        valueArray   EnumType values

[ruby] How to implement Enums in Ruby?

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