is there a hash equivalent to a custom 'class variables'? (ruby)

Question

I used hash of hashes to store settings in my code. I wonder if I can have something like class variable that is the same for all instances of the class for my @profile hash. So both profiles below would have general profile variable equal to both of them. I want the solution to use hash.

@profile = {
  "vB4Discussions" => {    #profile name
     "urls"  => ["vB4 General Discussions"],
     "process?" => false,
     "type" => 'Discussion'
   },
  "vB4Design".downcase => {          #profile name      
     "urls"  => ["vB4 Design and Graphics Discussions"],
     "process?" => false,
      "type" => 'Design'
   }
} 

Answer 1

One way is to use a constant for the common bits, like so:

#!/usr/bin/ruby1.8

require 'pp'

COMMON_PROFILE = {
  "urls"  => ["vB4 General Discussions"],
  "process?" => false,
  "type" => 'Discussion'
}

@profile = {
  "vB4Discussions" => COMMON_PROFILE,
  "vB4Design".downcase => COMMON_PROFILE,
}

pp @profile

# => {"vB4Discussions"=>
# =>   {"vB4Discussions"=>
# =>     {"urls"=>["vB4 General Discussions"],
# =>      "process?"=>false,
# =>      "type"=>"Discussion"}},
# =>  "vb4design"=>
# =>   {"vB4Discussions"=>
# =>     {"urls"=>["vB4 General Discussions"],
# =>      "process?"=>false,
# =>      "type"=>"Discussion"}}}

Answer 2

Assuming I understand your question:

Yes, Ruby has class variables (@@a_class_variable) but the preferred way is to use an instance variable of the singleton class:

class MyClass
  class << self  # open the single class
    attr_reader :profiles
  end

  @profiles = {
    #...
  }

  def foo
    if self.class.profiles["vB4Discussions"]["process?"]
      # process...
    end
  end
end

Answer 3

Did you know that hashes can have a special proc called when a key is not found?

This could be used here very nicely.

require "backports"  # Needed in Ruby 1.8.6
SETTINGS = {
  "default" => {
    "urls"  => [],
    "process?" => false,
    "type" => 'Discussion'
  },
  "vB4Discussions" => {
    "urls"  => ["vB4 General Discussions"],
  },
  "vB4Design".downcase => {
    "urls"  => ["vB4 Design and Graphics Discussions"],
    "type" => 'Design'
  }
}

# Use defaults 
SETTINGS["vb4design"].default_proc = lambda{|h, k| SETTINGS["default"][k]}
SETTINGS["vB4Discussions"].default_proc = lambda{|h, k| SETTINGS["default"][k]}

# Now the defaults are used if needed:
SETTINGS["vB4Discussions"]["type"]  # ==> 'Discussion'
SETTINGS["vB4Discussions"]["process?"]  # ==> false

# Defaults can be edited later:
SETTINGS["default"]["process?"] = true
SETTINGS["vB4Discussions"]["process?"]  # ==> true
SETTINGS["vb4design"]["process?"]  # ==> true

# Specific value can be changed too
SETTINGS["vb4design"]["process?"] = false # ==> true
SETTINGS["vB4Discussions"]["process?"] # ==> true

Note: Unless you have a valid reason to use strings, you should use symbols for your keys (i.e. :vB4Discussions instead of "vB4Discussions".

The Hash.default_proc= is new to Ruby 1.8.7, so you need to require "backports" to use it. If you don't want this, you could instead specify the default proc when creating the hashes as follows:

DEFAULTS = {
  "urls"  => [],
  "process?" => false,
  "type" => 'Discussion'
}

SETTINGS = {
  "default" => DEFAULTS,
  "vB4Discussions" => Hash.new{|h, k| DEFAULTS[k]}.merge!{
    "urls"  => ["vB4 General Discussions"],
  },
  "vB4Design".downcase => Hash.new{|h, k| DEFAULTS[k]}.merge!{
    "urls"  => ["vB4 Design and Graphics Discussions"],
    "type" => 'Design'
  }
}