Module: Rink::Delegation
Overview
Blatantly ripped from ActiveSupport and pasted here to avoid the extra dependency. Only applied to objects internal to Rink.
Instance Method Summary collapse
-
#delegate(*methods) ⇒ Object
Provides a delegate class method to easily expose contained objects’ methods as your own.
Instance Method Details
#delegate(*methods) ⇒ Object
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"
If the object to which you delegate can be nil, you may want to use the :allow_nil option. In that case, it returns nil instead of raising a NoMethodError exception:
class Foo
attr_accessor :bar
def initialize( = nil)
@bar =
end
delegate :zoo, :to => :bar
end
Foo.new.zoo # raises NoMethodError exception (you called nil.zoo)
class Foo
attr_accessor :bar
def initialize( = nil)
@bar =
end
delegate :zoo, :to => :bar, :allow_nil => true
end
Foo.new.zoo # returns nil
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# File 'lib/rink/delegation.rb', line 102 def delegate(*methods) = methods.pop unless .is_a?(Hash) && to = [:to] raise ArgumentError, "Delegation needs a target. Supply an options hash with a :to key as the last argument (e.g. delegate :hello, :to => :greeter)." end if [:prefix] == true && [:to].to_s =~ /^[^a-z_]/ raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method." end prefix = [:prefix] && "#{[:prefix] == true ? to : [:prefix]}_" file, line = caller.first.split(':', 2) line = line.to_i methods.each do |method| on_nil = if [:allow_nil] 'return' else %(raise "#{prefix}#{method} delegated to #{to}.#{method}, but #{to} is nil: \#{self.inspect}") end module_eval(<<-EOS, file, line) def #{prefix}#{method}(*args, &block) # def customer_name(*args, &block) #{to}.__send__(#{method.inspect}, *args, &block) # client.__send__(:name, *args, &block) rescue NoMethodError # rescue NoMethodError if #{to}.nil? # if client.nil? #{on_nil} else # else raise # raise end # end end # end EOS end end |