How to print std::tuple iteratively - c++

Question

Most samples of c++ books leverage recursively mechanism to print std::tuple.
Is it possible to print std::tuples iteratively by leverage sizeof...(Typename)?
For example, the function signature is like below:
template<typename... Ts>
constexpr void PrintTuple(std::tuple<Ts...>& tuple)
Then I could use sizeof...(Ts) to know how many elements in the tuple and then
I could use std::get< i >(tuple) to retrieve the individual element?

Answer 1

Here's one of the possible solutions:
#include <cstddef>
#include <iostream>
#include <tuple>
#include <type_traits>
#include <utility>
template <typename T, std::size_t ...I, typename F>
void tuple_foreach_impl(T &&tuple, std::index_sequence<I...>, F &&func)
{
// In C++17 we would use a fold expression here, but in C++14 we have to resort to this.
using dummy_array = int[];
dummy_array{(void(func(std::get<I>(tuple))), 0)..., 0};
}
template <typename T, typename F> void tuple_foreach(T &&tuple, F &&func)
{
constexpr int size = std::tuple_size<std::remove_reference_t<T>>::value;
tuple_foreach_impl(std::forward<T>(tuple), std::make_index_sequence<size>{},
std::forward<F>(func));
}
int main()
{
auto x = std::make_tuple("Meow", 1, 2.3);
tuple_foreach(x, [](auto &&value)
{
std::cout << value << ' ';
});
// Prints:
// Meow
// 1
// 2.3
}
With tuple_foreach making a proper printer should be simple.
template <typename T> void print_tuple(const T &tuple)
{
std::cout << '{';
tuple_foreach(tuple, [first = true](auto &value) mutable
{
if (!first)
std::cout << "; ";
else
first = 0;
std::cout << value;
});
std::cout << '}';
}
// ...
print_tuple(std::make_tuple("Meow", 1, 2.3)); // Prints `{Meow; 1; 2.3}`

Answer 2

c++20 makes everything very easy:
void print_tuple(auto&& t) noexcept
{
[&]<auto ...I>(std::index_sequence<I...>) noexcept
{
(
[&]() noexcept
{
if constexpr(I)
{
std::cout << ", ";
}
std::cout << std::get<I>(t);
}(),
...
);
std::cout << '\n';
}
(
std::make_index_sequence<
std::tuple_size_v<std::remove_cvref_t<decltype(t)>>
>()
);
}