diff options
Diffstat (limited to 'activesupport/lib/active_support/core_ext/module/delegation.rb')
| -rw-r--r-- | activesupport/lib/active_support/core_ext/module/delegation.rb | 118 |
1 files changed, 95 insertions, 23 deletions
diff --git a/activesupport/lib/active_support/core_ext/module/delegation.rb b/activesupport/lib/active_support/core_ext/module/delegation.rb index 24450cd221..4310df3024 100644 --- a/activesupport/lib/active_support/core_ext/module/delegation.rb +++ b/activesupport/lib/active_support/core_ext/module/delegation.rb @@ -1,15 +1,19 @@ -require 'set' +# frozen_string_literal: true + +require "set" +require "active_support/core_ext/regexp" class Module # Error generated by +delegate+ when a method is called on +nil+ and +allow_nil+ # option is not used. class DelegationError < NoMethodError; end + RUBY_RESERVED_KEYWORDS = %w(alias and BEGIN begin break case class def defined? do + else elsif END end ensure false for if in module next nil not or redo rescue retry + return self super then true undef unless until when while yield) + DELEGATION_RESERVED_KEYWORDS = %w(_ arg args block) DELEGATION_RESERVED_METHOD_NAMES = Set.new( - %w(_ arg args alias and BEGIN begin block break case class def defined? do - else elsif END end ensure false for if in module next nil not or redo - rescue retry return self super then true undef unless until when while - yield) + RUBY_RESERVED_KEYWORDS + DELEGATION_RESERVED_KEYWORDS ).freeze # Provides a +delegate+ class method to easily expose contained objects' @@ -18,7 +22,8 @@ class Module # ==== Options # * <tt>:to</tt> - Specifies the target object # * <tt>:prefix</tt> - Prefixes the new method with the target name or a custom prefix - # * <tt>:allow_nil</tt> - if set to true, prevents a +NoMethodError+ from being raised + # * <tt>:allow_nil</tt> - if set to true, prevents a +Module::DelegationError+ + # from being raised # # 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 @@ -110,18 +115,16 @@ class Module # invoice.customer_address # => 'Vimmersvej 13' # # 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. + # +Module::DelegationError+ is raised. If you wish to instead return +nil+, + # use the <tt>:allow_nil</tt> option. # # class User < ActiveRecord::Base # has_one :profile # delegate :age, to: :profile # end # - # User.new.age # raises NoMethodError: undefined method `age' + # User.new.age + # # => Module::DelegationError: User#age delegated to profile.age, but profile is nil # # But if not having a profile yet is fine and should not be an error # condition: @@ -148,33 +151,32 @@ class Module # Foo.new("Bar").name # raises NoMethodError: undefined method `name' # # The target method must be public, otherwise it will raise +NoMethodError+. - # def delegate(*methods, to: nil, prefix: nil, allow_nil: nil) unless 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).' + 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 =~ /^[^a-z_]/ - raise ArgumentError, 'Can only automatically set the delegation prefix when delegating to a method.' + if prefix == true && /^[^a-z_]/.match?(to) + raise ArgumentError, "Can only automatically set the delegation prefix when delegating to a method." end method_prefix = \ if prefix "#{prefix == true ? to : prefix}_" else - '' + "" end - file, line = caller(1, 1).first.split(':'.freeze, 2) - line = line.to_i + location = caller_locations(1, 1).first + file, line = location.path, location.lineno to = to.to_s to = "self.#{to}" if DELEGATION_RESERVED_METHOD_NAMES.include?(to) - methods.each do |method| + methods.map do |method| # Attribute writer methods only accept one argument. Makes sure []= # methods still accept two arguments. - definition = (method =~ /[^\]]=$/) ? 'arg' : '*args, &block' + definition = /[^\]]=$/.match?(method) ? "arg" : "*args, &block" # The following generated method calls the target exactly once, storing # the returned value in a dummy variable. @@ -191,7 +193,7 @@ class Module " _.#{method}(#{definition})", "end", "end" - ].join ';' + ].join ";" else exception = %(raise DelegationError, "#{self}##{method_prefix}#{method} delegated to #{to}.#{method}, but #{to} is nil: \#{self.inspect}") @@ -206,10 +208,80 @@ class Module " raise", " end", "end" - ].join ';' + ].join ";" end module_eval(method_def, file, line) end end + + # When building decorators, a common pattern may emerge: + # + # class Partition + # def initialize(event) + # @event = event + # end + # + # def person + # @event.detail.person || @event.creator + # end + # + # private + # def respond_to_missing?(name, include_private = false) + # @event.respond_to?(name, include_private) + # end + # + # def method_missing(method, *args, &block) + # @event.send(method, *args, &block) + # end + # end + # + # With <tt>Module#delegate_missing_to</tt>, the above is condensed to: + # + # class Partition + # delegate_missing_to :@event + # + # def initialize(event) + # @event = event + # end + # + # def person + # @event.detail.person || @event.creator + # end + # end + # + # The target can be anything callable within the object, e.g. instance + # variables, methods, constants, etc. + # + # The delegated method must be public on the target, otherwise it will + # raise +NoMethodError+. + def delegate_missing_to(target) + target = target.to_s + target = "self.#{target}" if DELEGATION_RESERVED_METHOD_NAMES.include?(target) + + module_eval <<-RUBY, __FILE__, __LINE__ + 1 + def respond_to_missing?(name, include_private = false) + # It may look like an oversight, but we deliberately do not pass + # +include_private+, because they do not get delegated. + + #{target}.respond_to?(name) || super + end + + def method_missing(method, *args, &block) + if #{target}.respond_to?(method) + #{target}.public_send(method, *args, &block) + else + begin + super + rescue NoMethodError + if #{target}.nil? + raise DelegationError, "\#{method} delegated to #{target}, but #{target} is nil" + else + raise + end + end + end + end + RUBY + end end |