I couldn't really find this in Rails documentation but it seems like 'mattr_accessor' is the Module corollary for 'attr_accessor' (getter & setter) in a normal Ruby class.
Eg. in a class
class User
attr_accessor :name
def set_fullname
@name = "#{self.first_name} #{self.last_name}"
end
end
Eg. in a module
module Authentication
mattr_accessor :current_user
def login
@current_user = session[:user_id] || nil
end
end
This helper method is provided by ActiveSupport.
Rails extends Ruby with both mattr_accessor
(Module accessor) and cattr_accessor
(as well as _reader
/_writer
versions). As Ruby's attr_accessor
generates getter/setter methods for instances, cattr/mattr_accessor
provide getter/setter methods at the class or module level. Thus:
module Config
mattr_accessor :hostname
mattr_accessor :admin_email
end
is short for:
module Config
def self.hostname
@hostname
end
def self.hostname=(hostname)
@hostname = hostname
end
def self.admin_email
@admin_email
end
def self.admin_email=(admin_email)
@admin_email = admin_email
end
end
Both versions allow you to access the module-level variables like so:
>> Config.hostname = "example.com"
>> Config.admin_email = "[email protected]"
>> Config.hostname # => "example.com"
>> Config.admin_email # => "[email protected]"