Module: ActiveSupport::Delegation

Defined in:
lib/active_support/delegation.rb

Overview

:nodoc:

Constant Summary collapse

RUBY_RESERVED_KEYWORDS = 
%w(__ENCODING__ __LINE__ __FILE__ 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)
RESERVED_METHOD_NAMES = 
(RUBY_RESERVED_KEYWORDS + %w(_ arg args block)).to_set.freeze

Class Method Summary collapse

Class Method Details

.generate(owner, methods, location: nil, to: nil, prefix: nil, allow_nil: nil, nilable: true, private: nil, as: nil, signature: nil) ⇒ Object

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# File 'lib/active_support/delegation.rb', line 21

def generate(owner, methods, location: nil, to: nil, prefix: nil, allow_nil: nil, nilable: true, private: nil, as: nil, signature: nil)
  unless to
    raise ArgumentError, "Delegation needs a target. Supply a keyword argument 'to' (e.g. delegate :hello, to: :greeter)."
  end

  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

  location ||= caller_locations(1, 1).first
  file, line = location.path, location.lineno

  receiver = if to.is_a?(Module)
    if to.name.nil?
      raise ArgumentError, "Can't delegate to anonymous class or module: #{to}"
    end

    unless Inflector.safe_constantize(to.name).equal?(to)
      raise ArgumentError, "Can't delegate to detached class or module: #{to.name}"
    end

    "::#{to.name}"
  else
    to.to_s
  end
  receiver = "self.#{receiver}" if RESERVED_METHOD_NAMES.include?(receiver)

  explicit_receiver = false
  receiver_class = if as
    explicit_receiver = true
    as
  elsif to.is_a?(Module)
    to.singleton_class
  elsif receiver == "self.class"
    nilable = false # self.class can't possibly be nil
    owner.singleton_class
  end

  method_def = []
  method_names = []

  method_def << "self.private" if private

  methods.each do |method|
    method_name = prefix ? "#{method_prefix}#{method}" : method
    method_names << method_name.to_sym

    # Attribute writer methods only accept one argument. Makes sure []=
    # methods still accept two arguments.
    definition = \
      if signature
        signature
      elsif /[^\]]=\z/.match?(method)
        "arg"
      else
        method_object = if receiver_class
          begin
            receiver_class.public_instance_method(method)
          rescue NameError
            raise if explicit_receiver
            # Do nothing. Fall back to `"..."`
          end
        end

        if method_object
          parameters = method_object.parameters

          if parameters.map(&:first).intersect?([:opt, :rest, :keyreq, :key, :keyrest])
            "..."
          else
            defn = parameters.filter_map { |type, arg| arg if type == :req }
            defn << "&"
            defn.join(", ")
          end
        else
          "..."
        end
      end

    # The following generated method calls 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 conceptually, from the user point of view, the delegator should
    # be doing one call.
    if nilable == false
      method_def <<
        "def #{method_name}(#{definition})" <<
        "  (#{receiver}).#{method}(#{definition})" <<
        "end"
    elsif allow_nil
      method = method.to_s

      method_def <<
        "def #{method_name}(#{definition})" <<
        "  _ = #{receiver}" <<
        "  if !_.nil? || nil.respond_to?(:#{method})" <<
        "    _.#{method}(#{definition})" <<
        "  end" <<
        "end"
    else
      method = method.to_s
      method_name = method_name.to_s

      method_def <<
        "def #{method_name}(#{definition})" <<
        "  _ = #{receiver}" <<
        "  _.#{method}(#{definition})" <<
        "rescue NoMethodError => e" <<
        "  if _.nil? && e.name == :#{method}" <<
        "    raise ::ActiveSupport::DelegationError.nil_target(:#{method_name}, :'#{receiver}')" <<
        "  else" <<
        "    raise" <<
        "  end" <<
        "end"
    end
  end
  owner.module_eval(method_def.join(";"), file, line)
  method_names
end

.generate_method_missing(owner, target, allow_nil: nil) ⇒ Object

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# File 'lib/active_support/delegation.rb', line 150

def generate_method_missing(owner, target, allow_nil: nil)
  target = target.to_s
  target = "self.#{target}" if RESERVED_METHOD_NAMES.include?(target) || target == "__target"

  if allow_nil
    owner.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.

        return false if name == :marshal_dump || name == :_dump
        #{target}.respond_to?(name) || super
      end

      def method_missing(method, ...)
        __target = #{target}
        if __target.nil? && !nil.respond_to?(method)
          nil
        elsif __target.respond_to?(method)
          __target.public_send(method, ...)
        else
          super
        end
      end
    RUBY
  else
    owner.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.

        return false if name == :marshal_dump || name == :_dump
        #{target}.respond_to?(name) || super
      end

      def method_missing(method, ...)
        __target = #{target}
        if __target.nil? && !nil.respond_to?(method)
          raise ::ActiveSupport::DelegationError.nil_target(method, :'#{target}')
        elsif __target.respond_to?(method)
          __target.public_send(method, ...)
        else
          super
        end
      end
    RUBY
  end
end