suppose I got a struct i.e. Coord
that contains two static member variables, then pass it as an argument of variadic template function variadic_print_coord()
, how do I unpack the variadic expressions, to call the print_pair()
function that shown below.
template<class T1, class T2>
void print_pair(T1 t1, T2 t2)
{
std::cout << t1 << " and " << t2 << '\n';
}
template<class T1, class T2, class ...Ts>
void print_pair(T1 t1, T2 t2, Ts... ts)
{
print_pair(t1, t2);
print_pair(ts... );
}
template<int X, int Y>
struct Coord
{
static const int valueX = X;
static const int valueY = Y;
}
template<class... COORDs>
void variadic_print_coord()
{
print_pair(COORD1::valueX, COORD1::valueY, COORD2::valueX, COORD2::valueY, ...,
COORDs::valueX, COORDs::valueY);
//how could I manipulating the pack expressions to get something like this
}
int main()
{
print_pair<Coord<0,1>, Coord<2,3>, Coord<4,5>>();
//result:
//0 and 1
//2 and 3
//4 and 5
}
many thanks!
CodePudding user response:
You can use the following construct involving a fold expression
template<class... COORDs>
void variadic_print_coord()
{
(print_pair(COORDs::X, COORDs::Y), ...);
}
In this case you won't need the variadic version of print_pair
, as the calls basically decouple.
#include <iostream>
template<class T1, class T2>
void print_pair(T1 t1, T2 t2)
{
std::cout << t1 << " and " << t2 << '\n';
}
template<int X, int Y>
struct Coord
{
static const int valueX = X;
static const int valueY = Y;
};
template<class... COORDs>
void variadic_print_coord()
{
(print_pair(COORDs::valueX, COORDs::valueY), ...);
}
int main()
{
variadic_print_coord<Coord<0,1>, Coord<2,3>, Coord<4,5>>();
//result:
//0 and 1
//2 and 3
//4 and 5
}