couchrest_model/lib/couchrest/support/class.rb

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# Copyright (c) 2004-2008 David Heinemeier Hansson
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject to
# the following conditions:
#
# The above copyright notice and this permission notice shall be
# included in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
# EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
# NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE
# LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION
# OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION
# WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
# Allows attributes to be shared within an inheritance hierarchy, but where
# each descendant gets a copy of their parents' attributes, instead of just a
# pointer to the same. This means that the child can add elements to, for
# example, an array without those additions being shared with either their
# parent, siblings, or children, which is unlike the regular class-level
# attributes that are shared across the entire hierarchy.
class Class
# Defines class-level and instance-level attribute reader.
#
# @param *syms<Array> Array of attributes to define reader for.
# @return <Array[#to_s]> List of attributes that were made into cattr_readers
#
# @api public
#
# @todo Is this inconsistent in that it does not allow you to prevent
# an instance_reader via :instance_reader => false
def cattr_reader(*syms)
syms.flatten.each do |sym|
next if sym.is_a?(Hash)
class_eval(<<-RUBY, __FILE__, __LINE__ + 1)
unless defined? @@#{sym}
@@#{sym} = nil
end
def self.#{sym}
@@#{sym}
end
def #{sym}
@@#{sym}
end
RUBY
end
end
# Defines class-level (and optionally instance-level) attribute writer.
#
# @param <Array[*#to_s, Hash{:instance_writer => Boolean}]> Array of attributes to define writer for.
# @option syms :instance_writer<Boolean> if true, instance-level attribute writer is defined.
# @return <Array[#to_s]> List of attributes that were made into cattr_writers
#
# @api public
def cattr_writer(*syms)
options = syms.last.is_a?(Hash) ? syms.pop : {}
syms.flatten.each do |sym|
class_eval(<<-RUBY, __FILE__, __LINE__ + 1)
unless defined? @@#{sym}
@@#{sym} = nil
end
def self.#{sym}=(obj)
@@#{sym} = obj
end
RUBY
unless options[:instance_writer] == false
class_eval(<<-RUBY, __FILE__, __LINE__ + 1)
def #{sym}=(obj)
@@#{sym} = obj
end
RUBY
end
end
end
# Defines class-level (and optionally instance-level) attribute accessor.
#
# @param *syms<Array[*#to_s, Hash{:instance_writer => Boolean}]> Array of attributes to define accessor for.
# @option syms :instance_writer<Boolean> if true, instance-level attribute writer is defined.
# @return <Array[#to_s]> List of attributes that were made into accessors
#
# @api public
def cattr_accessor(*syms)
cattr_reader(*syms)
cattr_writer(*syms)
end
# Defines class-level inheritable attribute reader. Attributes are available to subclasses,
# each subclass has a copy of parent's attribute.
#
# @param *syms<Array[#to_s]> Array of attributes to define inheritable reader for.
# @return <Array[#to_s]> Array of attributes converted into inheritable_readers.
#
# @api public
#
# @todo Do we want to block instance_reader via :instance_reader => false
# @todo It would be preferable that we do something with a Hash passed in
# (error out or do the same as other methods above) instead of silently
# moving on). In particular, this makes the return value of this function
# less useful.
def class_inheritable_reader(*ivars)
instance_reader = ivars.pop[:reader] if ivars.last.is_a?(Hash)
ivars.each do |ivar|
self.class_eval <<-RUBY, __FILE__, __LINE__ + 1
def self.#{ivar}
return @#{ivar} if self.object_id == #{self.object_id} || defined?(@#{ivar})
ivar = superclass.#{ivar}
return nil if ivar.nil? && !#{self}.instance_variable_defined?("@#{ivar}")
@#{ivar} = ivar && !ivar.is_a?(Module) && !ivar.is_a?(Numeric) && !ivar.is_a?(TrueClass) && !ivar.is_a?(FalseClass) && !ivar.is_a?(Symbol) ? ivar.dup : ivar
end
RUBY
unless instance_reader == false
self.class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{ivar}
self.class.#{ivar}
end
RUBY
end
end
end
# Defines class-level inheritable attribute writer. Attributes are available to subclasses,
# each subclass has a copy of parent's attribute.
#
# @param *syms<Array[*#to_s, Hash{:instance_writer => Boolean}]> Array of attributes to
# define inheritable writer for.
# @option syms :instance_writer<Boolean> if true, instance-level inheritable attribute writer is defined.
# @return <Array[#to_s]> An Array of the attributes that were made into inheritable writers.
#
# @api public
#
# @todo We need a style for class_eval <<-HEREDOC. I'd like to make it
# class_eval(<<-RUBY, __FILE__, __LINE__), but we should codify it somewhere.
def class_inheritable_writer(*ivars)
instance_writer = ivars.pop[:instance_writer] if ivars.last.is_a?(Hash)
ivars.each do |ivar|
self.class_eval <<-RUBY, __FILE__, __LINE__ + 1
def self.#{ivar}=(obj)
@#{ivar} = obj
end
RUBY
unless instance_writer == false
self.class_eval <<-RUBY, __FILE__, __LINE__ + 1
def #{ivar}=(obj) self.class.#{ivar} = obj end
RUBY
end
end
end
# Defines class-level inheritable attribute accessor. Attributes are available to subclasses,
# each subclass has a copy of parent's attribute.
#
# @param *syms<Array[*#to_s, Hash{:instance_writer => Boolean}]> Array of attributes to
# define inheritable accessor for.
# @option syms :instance_writer<Boolean> if true, instance-level inheritable attribute writer is defined.
# @return <Array[#to_s]> An Array of attributes turned into inheritable accessors.
#
# @api public
def class_inheritable_accessor(*syms)
class_inheritable_reader(*syms)
class_inheritable_writer(*syms)
end
end