assigning members of a pair to variables

Question

Is it possible to assign the members of a pair without creating a temporary object?

#include <tuple>
using namespace std;

pair< bool, int > foo()
{
    return make_pair( false, 3 );
}

int main()
{
    int x;
    bool y;

    auto z = foo();
    x = z.second;
    y = z.first;

    return 0;
}

In the above code, the object auto z is needed to "hold" the pair before dissecting it, but its creation might be expensive in the actual code.

Answer 1

Yes; std::tie was invented for this:

#include <tuple>
#include <iostream>

std::pair<bool, int> foo()
{
    return std::make_pair(false, 3);
}

int main()
{
    int x;
    bool y;

    std::tie(y, x) = foo();
    std::cout << x << ',' << y << '\n';
}

// Output: 3,0

(live demo)

Of course you are still going to have a temporary object somewhere (modulo constant optimisations), but this is the most direct you can write the code unless you initialise x and y directly from their eventual values rather than first creating a pair inside foo().