class Docile::FallbackContextProxy

@api private

A proxy object with a primary receiver as well as a secondary fallback receiver.

Will attempt to forward all method calls first to the primary receiver, and then to the fallback receiver if the primary does not handle that method.

This is useful for implementing DSL evaluation in the context of an object.

@see Docile.dsl_eval

Constants

NON_FALLBACK_METHODS

The set of methods which will not fallback from the block’s context to the dsl object.

NON_PROXIED_INSTANCE_VARIABLES

The set of instance variables which are local to this object and hidden. All other instance variables will be copied in and out of this object from the scope in which this proxy was created.

NON_PROXIED_METHODS

The set of methods which will not be proxied, but instead answered by this object directly.

Public Class Methods

new(receiver, fallback) click to toggle source

@param [Object] receiver the primary proxy target to which all methods

initially will be forwarded

@param [Object] fallback the fallback proxy target to which any methods

not handled by `receiver` will be forwarded
Calls superclass method
# File lib/docile/fallback_context_proxy.rb, line 42
def initialize(receiver, fallback)
  @__receiver__ = receiver
  @__fallback__ = fallback

  # Enables calling DSL methods from helper methods in the block's context
  unless fallback.respond_to?(:method_missing)
    # NOTE: There's no {#define_singleton_method} on Ruby 1.8.x
    singleton_class = (class << fallback; self; end)

    # instrument {#method_missing} on the block's context to fallback to
    # the DSL object. This allows helper methods in the block's context to
    # contain calls to methods on the DSL object.
    singleton_class.
      send(:define_method, :method_missing) do |method, *args, &block|
        m = method.to_sym
        if !NON_FALLBACK_METHODS.include?(m) && !fallback.respond_to?(m) && receiver.respond_to?(m)
          receiver.__send__(method.to_sym, *args, &block)
        else
          super(method, *args, &block)
        end
      end

    # instrument a helper method to remove the above instrumentation
    singleton_class.
      send(:define_method, :__docile_undo_fallback__) do
        singleton_class.send(:remove_method, :method_missing)
        singleton_class.send(:remove_method, :__docile_undo_fallback__)
      end
  end
end

Public Instance Methods

instance_variables() click to toggle source

@return [Array<Symbol>] Instance variable names, excluding

{NON_PROXIED_INSTANCE_VARIABLES}

@note on Ruby 1.8.x, the instance variable names are actually of

type `String`.
Calls superclass method
# File lib/docile/fallback_context_proxy.rb, line 78
def instance_variables
  # Ruby 1.8.x returns string names, convert to symbols for compatibility
  super.select { |v| !NON_PROXIED_INSTANCE_VARIABLES.include?(v.to_sym) }
end
method_missing(method, *args, &block) click to toggle source

Proxy all methods, excluding {NON_PROXIED_METHODS}, first to ‘receiver` and then to `fallback` if not found.

# File lib/docile/fallback_context_proxy.rb, line 85
def method_missing(method, *args, &block)
  if @__receiver__.respond_to?(method.to_sym)
    @__receiver__.__send__(method.to_sym, *args, &block)
  else
    @__fallback__.__send__(method.to_sym, *args, &block)
  end
end