module ActiveRecord::AttributeMethods::ClassMethods

def self.set_name_cache(name, value) 

def self.set_name_cache(name, value)
  const_name = "ATTR_#{name}"
  unless const_defined? const_name
    const_set const_name, value.dup.freeze
  end
end

def attribute_method?(attribute)

Person.attribute_method?(:nothing) # => false
Person.attribute_method?(:age=) # => true
Person.attribute_method?('name') # => true

end
class Person < ActiveRecord::Base

+false+ otherwise.
Returns +true+ if +attribute+ is an attribute method and table exists, 
def attribute_method?(attribute)
  super || (table_exists? && column_names.include?(attribute.to_s.sub(/=$/, '')))
end

def attribute_methods_generated? # :nodoc:

:nodoc: 
def attribute_methods_generated? # :nodoc:
  @attribute_methods_generated
end

def attribute_names

# => ["id", "created_at", "updated_at", "name", "age"]
Person.attribute_names

end
class Person < ActiveRecord::Base

table exists. Otherwise it returns an empty array.
Returns an array of column names as strings if it's not an abstract class and 
def attribute_names
  @attribute_names ||= if !abstract_class? && table_exists?
      column_names
    else
      []
    end
end

def dangerous_attribute_method?(name) # :nodoc:

:nodoc:
not by any ancestors. (So 'puts' is not dangerous but 'save' is.)
A method name is 'dangerous' if it is already defined by Active Record, but 
def dangerous_attribute_method?(name) # :nodoc:
  method_defined_within?(name, Base)
end

def define_attribute_methods # :nodoc:

:nodoc:
accessors, mutators and query methods.
Generates all the attribute related methods for columns in the database 
def define_attribute_methods # :nodoc:
  # Use a mutex; we don't want two thread simultaneously trying to define
  # attribute methods.
  generated_attribute_methods.synchronize do
    return if attribute_methods_generated?
    superclass.define_attribute_methods unless self == base_class
    super(column_names)
    @attribute_methods_generated = true
  end
end

def inherited(child_class) #:nodoc:

:nodoc: 
def inherited(child_class) #:nodoc:
  child_class.initialize_generated_modules
  super
end

def initialize_generated_modules # :nodoc:

:nodoc: 
def initialize_generated_modules # :nodoc:
  @generated_attribute_methods = Module.new {
    extend Mutex_m
    const_set :AttrNames, Module.new {
      def self.set_name_cache(name, value)
        const_name = "ATTR_#{name}"
        unless const_defined? const_name
          const_set const_name, value.dup.freeze
        end
      end
    }
  }
  @attribute_methods_generated = false
  include @generated_attribute_methods
end

def instance_method_already_implemented?(method_name)

# => false
Person.instance_method_already_implemented?(:name)

# => ActiveRecord::DangerousAttributeError: save is defined by ActiveRecord
Person.instance_method_already_implemented?(:save)

end
end
'already defined by Active Record'
def save
class Person < ActiveRecord::Base

\Active \Record method is defined in the model, otherwise +false+.
Raises a ActiveRecord::DangerousAttributeError exception when an 
def instance_method_already_implemented?(method_name)
  if dangerous_attribute_method?(method_name)
    raise DangerousAttributeError, "#{method_name} is defined by Active Record"
  end
  if superclass == Base
    super
  else
    # If B < A and A defines its own attribute method, then we don't want to overwrite that.
    defined = method_defined_within?(method_name, superclass, superclass.generated_attribute_methods)
    defined && !ActiveRecord::Base.method_defined?(method_name) || super
  end
end

def method_defined_within?(name, klass, sup = klass.superclass) # :nodoc:

:nodoc: 
def method_defined_within?(name, klass, sup = klass.superclass) # :nodoc:
  if klass.method_defined?(name) || klass.private_method_defined?(name)
    if sup.method_defined?(name) || sup.private_method_defined?(name)
      klass.instance_method(name).owner != sup.instance_method(name).owner
    else
      true
    end
  else
    false
  end
end

def undefine_attribute_methods # :nodoc:

:nodoc: 
def undefine_attribute_methods # :nodoc:
  super if attribute_methods_generated?
  @attribute_methods_generated = false
end