def exec_in_proxy_context(dsl, proxy_type, *args, &block)
      block_context = eval("self", block.binding)
      proxy_context = proxy_type.new(dsl, block_context)
      begin
        block_context.instance_variables.each do |ivar|
          value_from_block = block_context.instance_variable_get(ivar)
          proxy_context.instance_variable_set(ivar, value_from_block)
        end

        proxy_context.instance_exec(*args, &block)
      ensure
        if block_context.respond_to?(:__docile_undo_fallback__)
          block_context.send(:__docile_undo_fallback__)
        end

        block_context.instance_variables.each do |ivar|
          next unless proxy_context.instance_variables.include?(ivar)
          value_from_dsl_proxy = proxy_context.instance_variable_get(ivar)
          block_context.instance_variable_set(ivar, value_from_dsl_proxy)
        end
      end
    end
def exec_in_proxy_context(dsl, proxy_type, *args, &block)
      block_context = eval("self", block.binding)
      proxy_context = proxy_type.new(dsl, block_context)
      begin
        block_context.instance_variables.each do |ivar|
          value_from_block = block_context.instance_variable_get(ivar)
          proxy_context.instance_variable_set(ivar, value_from_block)
        end

        proxy_context.instance_exec(*args, &block)
      ensure
        if block_context.respond_to?(:__docile_undo_fallback__)
          block_context.send(:__docile_undo_fallback__)
        end

        block_context.instance_variables.each do |ivar|
          next unless proxy_context.instance_variables.include?(ivar)
          value_from_dsl_proxy = proxy_context.instance_variable_get(ivar)
          block_context.instance_variable_set(ivar, value_from_dsl_proxy)
        end
      end
    end
Execute a block in the context of an object whose methods represent the
 commands in a DSL, using a specific proxy class.

 @param dsl        [Object] context object whose methods make up the
                            (initial) DSL
 @param proxy_type [FallbackContextProxy, ChainingFallbackContextProxy]
                            which class to instantiate as proxy context
 @param args       [Array]  arguments to be passed to the block
 @param block      [Proc]   the block of DSL commands to be executed
 @return           [Object] the return value of the block