diff options
Diffstat (limited to 'activesupport')
| -rw-r--r-- | activesupport/lib/active_support/core_ext/module/delegation.rb | 72 | ||||
| -rw-r--r-- | activesupport/test/core_ext/module_test.rb | 31 |
2 files changed, 73 insertions, 30 deletions
diff --git a/activesupport/lib/active_support/core_ext/module/delegation.rb b/activesupport/lib/active_support/core_ext/module/delegation.rb index c0828343d8..e60f9a1fe6 100644 --- a/activesupport/lib/active_support/core_ext/module/delegation.rb +++ b/activesupport/lib/active_support/core_ext/module/delegation.rb @@ -1,8 +1,10 @@ class Module - # Provides a delegate class method to easily expose contained objects' public methods - # as your own. Pass one or more methods (specified as symbols or strings) - # and the name of the target object via the <tt>:to</tt> option (also a symbol - # or string). At least one method and the <tt>:to</tt> option are required. + # Provides a +delegate+ class method to easily expose contained objects' + # public methods as your own. + # + # The macro receives one or more method names (specified as symbols or + # strings) and the name of the target object via the <tt>:to</tt> option + # (also a symbol or string). # # Delegation is particularly useful with Active Record associations: # @@ -89,39 +91,40 @@ class Module # invoice.customer_name # => 'John Doe' # invoice.customer_address # => 'Vimmersvej 13' # - # If the delegate object is +nil+ an exception is raised, and that happens - # no matter whether +nil+ responds to the delegated method. You can get a - # +nil+ instead with the +:allow_nil+ option. + # If the target is +nil+ and does not respond to the delegated method a + # +NoMethodError+ is raised, as with any other value. Sometimes, however, it + # makes sense to be robust to that situation and that is the purpose of the + # <tt>:allow_nil</tt> option: If the target is not +nil+, or it is and + # responds to the method, everything works as usual. But if it is +nil+ and + # does not respond to the delegated method, +nil+ is returned. # - # class Foo - # attr_accessor :bar - # def initialize(bar = nil) - # @bar = bar - # end - # delegate :zoo, to: :bar + # class User < ActiveRecord::Base + # has_one :profile + # delegate :age, to: :profile # end # - # Foo.new.zoo # raises NoMethodError exception (you called nil.zoo) + # User.new.age # raises NoMethodError: undefined method `age' # - # class Foo - # attr_accessor :bar - # def initialize(bar = nil) - # @bar = bar - # end - # delegate :zoo, to: :bar, allow_nil: true + # But if not having a profile yet is fine and should not be an error + # condition: + # + # class User < ActiveRecord::Base + # has_one :profile + # delegate :age, to: :profile, allow_nil: true # end # - # Foo.new.zoo # returns nil + # User.new.age # nil # - # If the delegate object is not +nil+ or +false+ and the object doesn't - # respond to the delegated method it will raise an exception. + # Note that if the target is not +nil+ then the call is attempted regardless of the + # <tt>:allow_nil</tt> option, and thus an exception is still raised if said object + # does not respond to the method: # # class Foo # def initialize(bar) # @bar = bar # end # - # delegate :name, to: :@bar + # delegate :name, to: :@bar, :allow_nil => true # end # # Foo.new("Bar").name # raises NoMethodError: undefined method `name' @@ -156,22 +159,31 @@ class Module # methods still accept two arguments. definition = (method =~ /[^\]]=$/) ? 'arg' : '*args, &block' + # The following generated methods call the target exactly once, storing + # the returned value in a dummy variable. + # + # Reason is twofold: On one hand doing less calls is in general better. + # On the other hand it could be that the target has side-effects, + # whereas conceptualy, from the user point of view, the delegator should + # be doing one call. if allow_nil - module_eval(<<-EOS, file, line - 2) + module_eval(<<-EOS, file, line - 3) def #{method_prefix}#{method}(#{definition}) # def customer_name(*args, &block) - if #{to} || #{to}.respond_to?(:#{method}) # if client || client.respond_to?(:name) - #{to}.#{method}(#{definition}) # client.name(*args, &block) + _ = #{to} # _ = client + if !_.nil? || nil.respond_to?(:#{method}) # if !_.nil? || nil.respond_to?(:name) + _.#{method}(#{definition}) # _.name(*args, &block) end # end end # end EOS else exception = %(raise "#{self}##{method_prefix}#{method} delegated to #{to}.#{method}, but #{to} is nil: \#{self.inspect}") - module_eval(<<-EOS, file, line - 1) + module_eval(<<-EOS, file, line - 2) def #{method_prefix}#{method}(#{definition}) # def customer_name(*args, &block) - #{to}.#{method}(#{definition}) # client.name(*args, &block) + _ = #{to} # _ = client + _.#{method}(#{definition}) # _.name(*args, &block) rescue NoMethodError # rescue NoMethodError - if #{to}.nil? # if client.nil? + if _.nil? # if _.nil? #{exception} # # add helpful message to the exception else # else raise # raise diff --git a/activesupport/test/core_ext/module_test.rb b/activesupport/test/core_ext/module_test.rb index 9a8582075d..8872611fb1 100644 --- a/activesupport/test/core_ext/module_test.rb +++ b/activesupport/test/core_ext/module_test.rb @@ -82,6 +82,21 @@ class Name end end +class SideEffect + attr_reader :ints + + delegate :to_i, :to => :shift, :allow_nil => true + delegate :to_s, :to => :shift + + def initialize + @ints = [1, 2, 3] + end + + def shift + @ints.shift + end +end + class ModuleTest < ActiveSupport::TestCase def setup @david = Someone.new("David", Somewhere.new("Paulina", "Chicago")) @@ -171,6 +186,12 @@ class ModuleTest < ActiveSupport::TestCase assert_nil rails.name end + # Ensures with check for nil, not for a falseish target. + def test_delegation_with_allow_nil_and_false_value + project = Project.new(false, false) + assert_raise(NoMethodError) { project.name } + end + def test_delegation_with_allow_nil_and_invalid_value rails = Project.new("Rails", "David") assert_raise(NoMethodError) { rails.name } @@ -233,6 +254,16 @@ class ModuleTest < ActiveSupport::TestCase "[#{e.backtrace.inspect}] did not include [#{file_and_line}]" end + def test_delegation_invokes_the_target_exactly_once + se = SideEffect.new + + assert_equal 1, se.to_i + assert_equal [2, 3], se.ints + + assert_equal '2', se.to_s + assert_equal [3], se.ints + end + def test_parent assert_equal Yz::Zy, Yz::Zy::Cd.parent assert_equal Yz, Yz::Zy.parent |