C++ std::function: To wrap any element that is callable Storing function arguments in std::tuple
Example
Some programs need so store arguments for future calling of some function.
This example shows how to call any function with arguments stored in std::tuple
#include <iostream>
#include <functional>
#include <tuple>
#include <iostream>
// simple function to be called
double foo_fn(int x, float y, double z)
{
double res = x + y + z;
std::cout << "foo_fn called. x = " << x << " y = " << y << " z = " << z
<< " res=" << res;
return res;
}
// helpers for tuple unrolling
template<int ...> struct seq {};
template<int N, int ...S> struct gens : gens<N-1, N-1, S...> {};
template<int ...S> struct gens<0, S...>{ typedef seq<S...> type; };
// invocation helper
template<typename FN, typename P, int ...S>
double call_fn_internal(const FN& fn, const P& params, const seq<S...>)
{
return fn(std::get<S>(params) ...);
}
// call function with arguments stored in std::tuple
template<typename Ret, typename ...Args>
Ret call_fn(const std::function<Ret(Args...)>& fn,
const std::tuple<Args...>& params)
{
return call_fn_internal(fn, params, typename gens<sizeof...(Args)>::type());
}
int main(void)
{
// arguments
std::tuple<int, float, double> t = std::make_tuple(1, 5, 10);
// function to call
std::function<double(int, float, double)> fn = foo_fn;
// invoke a function with stored arguments
call_fn(fn, t);
}
Output:
foo_fn called. x = 1 y = 5 z = 10 res=16
