piecewise_construct<T>(): Construct a T from tuple elements

example.cpp

#include "piecewise_construct.hpp"

struct foo
{
    foo(int i, int j) :
      i{i}, j{j}
    {}
    
    int i = 0, j = 0;
};

int main()
{
    auto f = piecewise_construct<foo>(std::make_tuple(1,2));
}

piecewise_construct.hpp

#include <tuple>
#include <type_traits>

template<typename T, typename... Ts, std::size_t... Is>
T piecewise_construct_impl(const std::tuple<Ts...>& args, std::index_sequence<Is...>)
{
    return { std::forward<std::decay_t<Ts>>(std::get<Is>(args))... };   
}

template<typename T, typename... Ts>
T piecewise_construct(const std::tuple<Ts...>& args)
{
    return piecewise_construct_impl<T>(args, std::index_sequence_for<Ts...>{});   
}