# File lib/aws/simple_db/item_collection.rb, line 623
      def replace_named_placeholders(orig_str, str, named)
        named.each do |name, value|
          str = str.gsub(name.to_sym.inspect, coerce_substitution(value))
        end
        str.scan(/:\S+/) do |missing|
          if orig_str.include?(missing)
            raise ArgumentError.new("missing value for placeholder #{missing}")
          end
        end
        str
      end