Python-like Iterable Unpacking in C++

Question

In python, we can unpack an iterable with a unary * like so:

def foo(a, b, c):
    ...

t = (1, 2, 3)
foo(*t)

In C++, I haven't encountered an equivalent. I'm aware that I could use structured bindings to solve a similar problem:

void foo(std::tuple<int, int, int> param)
{
    auto [a, b, c] = param;
    ...
}

But for the sake of curiosity, what if I wanted my function signature to accept three ints instead? Is there an elegant way of unpacking an iterator or a collection into the parameters of a function call?

Answer 1

For arrays you can use std::tuple_cat + std::apply like this: (Live demo)

#include <array>
#include <tuple>
#include <utility>
#include <iostream>
#include <format>

void f(int a,int b,int c)
{
    std::cout << std::format("{}, {}, {}\n", a, b, c);
}

int main()
{
    std::array<int,3> arguments{1,2,3};
    std::apply(f, std::tuple_cat(arguments));
}

Note, this only works if the size of the data is known at compile time.