I trying to write a function (call it apply_args()) that takes a specific function or function object and arguments for calling this object, and calls it using the perfect forwarding.
Example:
auto fun = [](std::string a, std::string const& b) { return a += b; };
std::string s("world!");
// s is passing by lvalue ref,
// temporary object by rvalue ref
s = apply_args(fun, std::string("Hello, "), s);
How can I implement that function?
template <typename Func, typename ...Args>
decltype(auto) apply_args(Func &&f, Args &&...args) {
return f(std::forward<Args>(args)...);
}
If you accept to pass the fun lambda as +fun (transforming it in a function pointer), I suppose you can simply write apply_args() as
template <typename R, typename ... Fts, typename ... As>
R apply_args (R(*fn)(Fts...), As && ... as)
{ return fn(std::forward<As>(as)...); }
The full example
#include <string>
#include <iostream>
#include <functional>
template <typename R, typename ... Fts, typename ... As>
R apply_args (R(*fn)(Fts...), As && ... as)
{ return fn(std::forward<As>(as)...); }
int main ()
{
auto fun = [](std::string a, std::string const& b) { return a += b; };
std::string s("world!");
s = apply_args(+fun, std::string("Hello, "), s);
std::cout << s << std::endl;
}