@SuppressWarnings("unchecked")
    public AsyncProcessFunction<Object, TBase<?, ?>, Object> asyncFunc() {
        return (AsyncProcessFunction<Object, TBase<?, ?>, Object>) func;
    }
Returns the {@link AsyncProcessFunction}.

@throws ClassCastException if this function is synchronous
thrift/thrift0.13/src/main/java/com/linecorp/armeria/internal/common/thrift/ThriftFunction.java