Array#to_hash converts an array of instances into a hash using the provided pair of methods to determine the key & value of each row

to_hash.rb

# example class
class State < Struct.new(:name, :code)
  def self.all
    [
      State.new('Alabama', 'AL'),
      State.new('Alaska',  'AK'),
      State.new('Arizona', 'AZ')
    ]
  end
end

# the magical Array#to_hash extension
class Array
  def to_hash(hash)
    key, value = hash.first
    self.reduce({}) do |hash, member|
      hash.merge(member.send(key) => member.send(value))
    end
  end
end


State.all.to_hash(:code => :name)
#=> { 'AL' => 'Alabama', 'AK' => 'Alaska', 'AZ' => 'Arizona' }