public FunctionScoreFunction <T> Exp(Expression <Func <T, object> > objectPath, Action <FunctionScoreDecayFieldDescriptor> descriptorBuilder)
        {
            var fn = new ExpFunction <T>(objectPath, descriptorBuilder);

            this._Functions.Add(fn);
            return(fn);
        }
        public FunctionScoreFunction <T> Exp(string field, Action <FunctionScoreDecayFieldDescriptor> descriptorBuilder)
        {
            var fn = new ExpFunction <T>(field, descriptorBuilder);

            this._Functions.Add(fn);
            return(fn);
        }