Provides a delegate class method to
easily expose contained objects’ methods as your own. Pass one or
more methods (specified as symbols or strings) and the name of the target
object as the final :to option (also a symbol or string). At least
one method and the :to option are required.
Delegation is particularly useful with Active Record associations:
class Greeter < ActiveRecord::Base
def hello() "hello" end
def goodbye() "goodbye" end
end
class Foo < ActiveRecord::Base
belongs_to :greeter
delegate :hello, :to => :greeter
end
Foo.new.hello # => "hello"
Foo.new.goodbye # => NoMethodError: undefined method `goodbye' for #<Foo:0x1af30c>
Multiple delegates to the same target are allowed:
class Foo < ActiveRecord::Base
belongs_to :greeter
delegate :hello, :goodbye, :to => :greeter
end
Foo.new.goodbye # => "goodbye"
Methods can be delegated to instance variables, class variables, or
constants by providing them as a symbols:
class Foo
CONSTANT_ARRAY = [0,1,2,3]
@@class_array = [4,5,6,7]
def initialize
@instance_array = [8,9,10,11]
end
delegate :sum, :to => :CONSTANT_ARRAY
delegate :min, :to => :@@class_array
delegate :max, :to => :@instance_array
end
Foo.new.sum # => 6
Foo.new.min # => 4
Foo.new.max # => 11
Delegates can optionally be prefixed using the :prefix option. If
the value is true, the delegate
methods are prefixed with the name of the object being delegated to.
Person = Struct.new(:name, :address)
class Invoice < Struct.new(:client)
delegate :name, :address, :to => :client, :prefix => true
end
john_doe = Person.new("John Doe", "Vimmersvej 13")
invoice = Invoice.new(john_doe)
invoice.client_name # => "John Doe"
invoice.client_address # => "Vimmersvej 13"
It is also possible to supply a custom prefix.
class Invoice < Struct.new(:client)
delegate :name, :address, :to => :client, :prefix => :customer
end
invoice = Invoice.new(john_doe)
invoice.customer_name # => "John Doe"
invoice.customer_address # => "Vimmersvej 13"