How to efficiently implement assign a vector's data to a number of variables?

Question

For example

void assign(vector<int> const& v, int a, float b)
{
    a = v[0];
    b = (float)v[1];
}

Here the value types doesn't need to be same. I want to make a function to assign variable number of variables. I can use variadic function. But I think using parameter pack may be more efficient. How to implement it? Thanks!

Answer 1

Fold expressions to the rescue!

template <typename ...P> void assign(const std::vector<int> &v, P &... params)
{
    std::size_t index = 0;
    (void(params = static_cast<P>(v[index++])) , ...);
}

If if has to be in C++11, you could use the dummy array trick:

template <typename ...P> void assign(const std::vector<int> &v, P &... params)
{
    std::size_t index = 0;
    using dummy = int[];
    (void)dummy{0, (void(params = static_cast<P>(v[index++])), 0) ...};
}