Using YAML as a parameter hash in Ruby

Posted August 11th, 2009 at 2:04 pm

Sometimes while coding Ruby applications the need develops to have some sort of metadata available as a configuration file. I have written some Ruby code that allows parameters that exist in a yaml file to be used as though they are in the class itself. In addition, I required code that allows the class to modify these parameters and then save them back to the file. Ruby's method_missing is a major player here. Anyway, I thought I would share this code.

To give an example of what exactly this does, assume that there exists a file called 'config.yml' that contains some key value pair such as :name => 'Bob':

--- 
:name: Bob

Using this class, we could do stuff like:

require 'boilerplate'
 
class Test < Boilerplate
  def run
    puts "Name is: #{name}"
    super
  end
end
 
t = Test.new
puts t.name       #=> 'Bob'
t.name = 'Joe'
puts t.name       #=> 'Joe'
t.run             #=> 'Name is: Joe'

Which would result in the yaml file now having the key value pair of :name => 'Joe'. If you didn't want to call 'run' you could call flush manually or add it as a call to some other method.

Here is the boilerplate.rb code in full:

class Boilerplate
  require 'yaml'
  require 'ftools'
 
  CACHE_LOCATION  = File.join('.')
  CACHE_FILE      = 'config.yml'
  CACHE_PATH      = File.join(File.expand_path(CACHE_LOCATION), CACHE_FILE)
 
  def initialize
    ensure_cache_exists
    load_settings
  end
 
  def run
    # do stuff here
    flush
  end
 
  private
 
  def method_missing(symbol, *args, &block)
    string = symbol.to_s # need for '=' method
 
    if @options.key?(symbol)
      @options[symbol]
    elsif string.index('=') + 1 == string.length && @options.key?(string.gsub('=', '').intern)
      @options[string.gsub('=', '').intern] = *args
    else
      super(symbol, *args, &block)
    end
  end
 
  def load_settings
    @options = {}
    imports = YAML.load_file(CACHE_PATH)
    if imports
      imports.each_pair do |key, value|
        if not key.is_a? Symbol
          imports[key.to_sym] = value
          imports.delete(key)
        end
      end
 
      @options = imports.merge(@options)
      end
    end
 
  def ensure_cache_exists
    File.makedirs(CACHE_LOCATION)
    File.new(CACHE_PATH, 'a+') unless File.exists?(CACHE_PATH) 
  end
 
  def flush
    File.open(CACHE_PATH, 'w') do |f|
      f.puts(YAML::dump(@options))
    end
  end
end

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Using YAML as a parameter hash in Ruby

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