method

delegate_missing_to

Ruby on Rails latest stable (v7.1.3.2) - 0 notes - Class: Module

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What's this?

delegate_missing_to(target, allow_nil: nil) public

When building decorators, a common pattern may emerge:

class Partition
  def initialize(event)
    @event = event
  end

  def person
    detail.person || 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 Module#delegate_missing_to, the above is condensed to:

class Partition
  delegate_missing_to :@event

  def initialize(event)
    @event = event
  end

  def person
    detail.person || 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 DelegationError. If you wish to instead return nil, use the :allow_nil option.

The marshal_dump and _dump methods are exempt from delegation due to possible interference when calling Marshal.dump(object), should the delegation target method of object add or remove instance variables.

Show source

# File activesupport/lib/active_support/core_ext/module/delegation.rb, line 318
  def delegate_missing_to(target, allow_nil: nil)
    target = target.to_s
    target = "self.#{target}" if DELEGATION_RESERVED_METHOD_NAMES.include?(target)

    module_eval       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, *args, &block)        if #{target}.respond_to?(method)          #{target}.public_send(method, *args, &block)        else          begin            super          rescue NoMethodError            if #{target}.nil?              if #{allow_nil == true}                nil              else                raise DelegationError, "\#{method} delegated to #{target}, but #{target} is nil"              end            else              raise            end          end        end      end      ruby2_keywords(:method_missing), __FILE__, __LINE__ + 1
  end

delegate_missing_to

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