Class: Module

Inherits:
Object
  • Object
show all
Defined in:
lib/attr_enum.rb

Overview

attr_enum

A macro to define an enumeration variable See en.wikipedia.org/wiki/Enumerated_type for more info

Usage

require 'rubygems'
require 'attr_enum'

class Card
  attr_enum :suit, %w( clubs hearts diamonds spades )
end

c = Card.new
c.suit = 'clubs'                                                                    
c.suit
=> 'clubs'
m.suit = 'jack' 
=> EnumeratedTypeError, Card.suit must be one of clubs, hearts, diamonds, spades.

Instance Method Summary collapse

Instance Method Details

#attr_enum(name, types) ⇒ Object

Declare an enumerated type which creates:

  • a class constant

  • a reader attribute

  • a writer with type constraint

Arguments

name

the name of the enumerated type, e.g :suit

types

an array of valid types, e.g. %w( clubs hearts diamonds spades )

Example

class Card
  attr_enum :suit, %w( clubs hearts diamonds spades )
end

Class constant

Card::SUITS
=> ["clubs", "hearts", "diamonds", "spades"]

reader/writer attributes

c = Card.new
c.suit = 'clubs'
c.suit
=> 'clubs'

Error handling:

Card.new.suit = 'spades' 
=> EnumeratedTypeError, Card.suit must be one of clubs, hearts, diamonds, spades.



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# File 'lib/attr_enum.rb', line 43

def attr_enum(name, types)
  attr_reader name                                                                  
                                                                                                        
  class_eval do
    # Create a class constant                                                          
    const_set :"#{name.to_s.upcase}_TYPES", types
    
    define_method(:"#{name}=") do |type|
      # Add type constraint to setter method                                          
      if self.class.const_get(:"#{name.to_s.upcase}_TYPES").include?(type)
        instance_variable_set :"@#{name}", type
      else
        raise EnumeratedTypeError, "Invalid type; must be one of #{types.join(', ')}."
      end
    end
  end
end