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require 'set'
module Docile
# @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
class FallbackContextProxy
# The set of methods which will **not** be proxied, but instead answered
# by this object directly.
NON_PROXIED_METHODS = Set[:__send__, :object_id, :__id__, :==, :equal?,
:'!', :'!=', :instance_exec, :instance_variables,
:instance_variable_get, :instance_variable_set,
:remove_instance_variable]
# 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_INSTANCE_VARIABLES = Set[:@__receiver__, :@__fallback__]
# Undefine all instance methods except those in {NON_PROXIED_METHODS}
instance_methods.each do |method|
undef_method(method) unless NON_PROXIED_METHODS.include?(method.to_sym)
end
# @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
def initialize(receiver, fallback)
@__receiver__ = receiver
@__fallback__ = fallback
end
# @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`.
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
# Proxy all methods, excluding {NON_PROXIED_METHODS}, first to `receiver`
# and then to `fallback` if not found.
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
end
end
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