Hash with set operations

hash-sets.rb

#
# The original idea was to use set operations to help dealing with a method's "options" hash.
#
# However, since I can't override || and &&, I wasn't able to figure out reasonable semantics.
#
# Therefore, I implemented `with_defaults`, which is what you want most of the time, and then
# wrote some thoughts about how set operations might work.
#

class Hash
  
  #
  # Fills in defaults that don't exist, and removes keys that aren't allowed.
  #
  # Example:
  #
  #    options = { 
  #      :opt1 => "Hey!", 
  #      :opt2 => "what", 
  #      :opt3 => nil,     # explicitly defined nils override defaults.
  #      :badopt => 6666   # this will be exluded, since it's not defined in the defaults.
  #    }
  #
  #    p options.with_defaults( 
  #        :opt1 => nil, 
  #        :opt2 => "Amazing.", 
  #        :opt3 => 3.14159265358979323846264338327950, 
  #        :opt4 => 42
  #      )
  #
  # Output:
  #
  #    {:opt1=>"Hey!", :opt2=>"what", :opt3=>nil, :opt4=>42}
  #
  def with_defaults(defaults)
    valid     = defaults.keys
    supplied  = keys & valid
    
    result    = defaults.dup
    
    supplied.each do |k|
      result[k] = self[k]
    end
    
    result
  end
    
  def +(other)
    # merge the two hashes (and union their sets of values)
  end
  
  def -(other)
    # subtract the hashes (and subtract their sets of values)
  end
  
  def &(other)
    # intersect the hashes (include key/value pairs that are identical)
  end
  
  def |(other)
    # overlay "other" onto self (replacing self's values with other's)
  end
  
  def ^(other)
    # find keys that are unique to each hash
  end
    
end


options = { 
  :opt1 => "Hey!", 
  :opt2 => "what", 
  :opt3 => nil,     # explicitly defined nils override defaults.
  :badopt => 6666   # this will be exluded, since it's not defined in the defaults.
}

p options.with_defaults( 
    :opt1 => nil, 
    :opt2 => "Amazing.", 
    :opt3 => 3.14159265358979323846264338327950, 
    :opt4 => 42
  )