//size_t I = 0 means the default value of I is 0(index of tuple is zero)
template<size_t I = 0, typename DataType, typename... Tp>
void Forward(const DataType& input, std::tuple<Tp...>& network)
{
    //set the value of InputParameter of network
    std::get<I>(network).InputParameter() = input;

    //call the forward function of network
    std::get<I>(network).Forward(std::get<I>(network).InputParameter(),
                           std::get<I>(network).OutputParameter());

    //now, we start the recursive, increment the I by 1
    ForwardTail<I + 1, Tp...>(network);
}

//size_t I = 1 means the default value of I is 0(index of tuple is one)
//we use std::enable_if to specify the case when the sizeof the tuple
//are same as I. In short, std::enable_if<I==sizeof...(Tp), void>::type
//tell the compiler---when the I == sizeof tuple(network), you should
//call(instantiate) this function, else call another(if exist).
//This function it the end condition of the Forawrd too
template<size_t I = 1, typename... Tp>
typename std::enable_if<I == sizeof...(Tp), void>::type
ForwardTail(std::tuple<Tp...>& network)
{
    LinkParameter(network);
}


//This function only instantiate if I < sizeof tuple(network)
//We use std::enable_if to specialize(do some "overload" at compile time)
//the function
template<size_t I = 1, typename... Tp>
typename std::enable_if<I < sizeof...(Tp), void>::type
ForwardTail(std::tuple<Tp...>& network)
{
    std::get<I>(network).Forward(std::get<I - 1>(network).OutputParameter(),
        std::get<I>(network).OutputParameter());

    //recursive call, this time we add the index by 1
    ForwardTail<I + 1, Tp...>(network);
}