Question

The following didactic example illustrates my problem :

#include <iostream>
#include <cmath>

template<class Function, class... Args>
double apply(Function f, Args... args)
{
    return f(args...);
}

template<class Function, class... Args>
double applybis(Function f, Args... args)
{
    return f(std::sin(args...));// <- How to apply a function to 
                                // each variadic parameter and 
                                // return a modified variadic list ?
}

int main(int argc, char* argv[])
{
    std::cout<<apply(static_cast<double(*)(double)>(std::sin), 3.)<<std::endl;
    return 0;
}

How to “transform” a variadic list by applying a function to each component and return a modified variadic list ?
(Is there a way to write the applybis function without modifying its current signature ?)

Answer 1

Here you go:

return f(std::sin(args)...);

That is, ... should come after (args).

It expands/unpacks to this form:

return f( std::sin(arg0), std::sin(arg1), ......, std::sin(argN) );