Ruby::Enum
==========
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Enum-like behavior for Ruby, heavily inspired by [this](http://www.rubyfleebie.com/enumerations-and-ruby), and improved upon [another blog post](http://code.dblock.org/how-to-define-enums-in-ruby).
## Table of Contents
- [Usage](#usage)
- [Constants](#constants)
- [Class Methods](#class-methods)
- [Default Value](#default-value)
- [Enumerating](#enumerating)
- [Iterating](#iterating)
- [Mapping](#mapping)
- [Reducing](#reducing)
- [Sorting](#sorting)
- [Hashing](#hashing)
- [Retrieving keys and values](#retrieving-keys-and-values)
- [Mapping keys to values](#mapping-keys-to-values)
- [Mapping values to keys](#mapping-values-to-keys)
- [Duplicate enumerator keys or duplicate values](#duplicate-enumerator-keys-or-duplicate-values)
- [Inheritance](#inheritance)
- [Contributing](#contributing)
- [Copyright and License](#copyright-and-license)
- [Related Projects](#related-projects)
## Usage
Enums can be defined and accessed either as constants, or class methods, which is a matter of preference.
### Constants
Define enums, and reference them as constants.
``` ruby
class OrderState
include Ruby::Enum
define :CREATED, 'created'
define :PAID, 'paid'
end
```
``` ruby
OrderState::CREATED # 'created'
OrderState::PAID # 'paid'
OrderState::UNKNOWN # raises Ruby::Enum::Errors::UninitializedConstantError
OrderState.keys # [ :CREATED, :PAID ]
OrderState.values # [ 'created', 'paid' ]
OrderState.to_h # { :CREATED => 'created', :PAID => 'paid' }
```
### Class Methods
Define enums, and reference them as class methods.
``` ruby
class OrderState
include Ruby::Enum
define :created, 'created'
define :paid, 'paid'
end
```
```ruby
OrderState.created # 'created'
OrderState.paid # 'paid'
OrderState.undefined # NoMethodError is raised
OrderState.keys # [ :created, :paid ]
OrderState.values # ['created', 'paid']
OrderState.to_h # { :created => 'created', :paid => 'paid' }
```
### Default Value
The value is optional. If unspecified, the value will default to the key.
``` ruby
class OrderState
include Ruby::Enum
define :UNSPECIFIED
define :unspecified
end
```
``` ruby
OrderState::UNSPECIFIED # :UNSPECIFIED
OrderState.unspecified # :unspecified
```
### Enumerating
Enums support all `Enumerable` methods.
#### Iterating
``` ruby
OrderState.each do |key, enum|
# key and enum.key are :CREATED, :PAID
# enum.value is 'created', 'paid'
end
```
``` ruby
OrderState.each_key do |key|
# :CREATED, :PAID
end
```
``` ruby
OrderState.each_value do |value|
# 'created', 'paid'
end
```
#### Mapping
``` ruby
OrderState.map do |key, enum|
# key and enum.key are :CREATED, :PAID
# enum.value is 'created', 'paid'
[enum.value, key]
end
# => [ ['created', :CREATED], ['paid', :PAID] ]
```
#### Reducing
``` ruby
OrderState.reduce([]) do |arr, (key, enum)|
# key and enum.key are :CREATED, :PAID
# enum.value is 'created', 'paid'
arr << [enum.value, key]
end
# => [ ['created', :CREATED], ['paid', :PAID] ]
```
#### Sorting
``` ruby
OrderState.sort_by do |key, enum|
# key and enum.key are :CREATED, :PAID
# enum.value is 'created', 'paid'
enum.value.length
end
# => [[:PAID, #<OrderState:0x0 @key=:PAID, @value="paid">], [:CREATED, #<OrderState:0x1 @key=:CREATED, @value="created">]]
```
### Hashing
Several hash-like methods are supported.
#### Retrieving keys and values
``` ruby
OrderState.keys
# => [:CREATED, :PAID]
OrderState.values
# => ['created', 'paid']
```
#### Mapping keys to values
``` ruby
OrderState.key?(:CREATED)
# => true
OrderState.value(:CREATED)
# => 'created'
OrderState.key?(:FAILED)
# => false
OrderState.value(:FAILED)
# => nil
```
#### Mapping values to keys
``` ruby
OrderState.value?('paid')
# => true
OrderState.key('paid')
# => :PAID
OrderState.value?('failed')
# => false
OrderState.key('failed')
# => nil
```
### Duplicate enumerator keys or duplicate values
Defining duplicate enums raises `Ruby::Enum::Errors::DuplicateKeyError`.
```ruby
class OrderState
include Ruby::Enum
define :CREATED, 'created'
define :CREATED, 'recreated' # raises DuplicateKeyError
end
```
Defining a duplicate value raises `Ruby::Enum::Errors::DuplicateValueError`.
```ruby
class OrderState
include Ruby::Enum
define :CREATED, 'created'
define :RECREATED, 'created' # raises DuplicateValueError
end
```
The `DuplicateValueError` exception is raised to be consistent with the unique key constraint. Since keys are unique, there needs to be a way to map values to keys using `OrderState.value('created')`.
### Inheritance
When inheriting from a `Ruby::Enum` class, all defined enums in the parent class will be accessible in sub classes as well. Sub classes can also provide extra enums, as usual.
``` ruby
class OrderState
include Ruby::Enum
define :CREATED, 'CREATED'
define :PAID, 'PAID'
end
class ShippedOrderState < OrderState
define :PREPARED, 'PREPARED'
define :SHIPPED, 'SHIPPED'
end
```
``` ruby
ShippedOrderState::CREATED # 'CREATED'
ShippedOrderState::PAID # 'PAID'
ShippedOrderState::PREPARED # 'PREPARED'
ShippedOrderState::SHIPPED # 'SHIPPED'
```
The `values` class method will enumerate the values from all base classes.
``` ruby
OrderState.values # ['CREATED', 'PAID']
ShippedOrderState.values # ['CREATED', 'PAID', 'PREPARED', SHIPPED']
```
## Contributing
You're encouraged to contribute to ruby-enum. See [CONTRIBUTING](CONTRIBUTING.md) for details.
## Copyright and License
Copyright (c) 2013-2021, Daniel Doubrovkine and [Contributors](CHANGELOG.md).
This project is licensed under the [MIT License](LICENSE.md).
## Related Projects
* [typesafe_enum](https://github.com/dmolesUC3/typesafe_enum): Typesafe enums, inspired by Java.
* [renum](https://github.com/duelinmarkers/renum): A readable, but terse enum.
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