Next generation of std::tie

Question

When a function need to return two parameters you can write it using a std::pair:

std::pair<int, int> f()
{return std::make_pair(1,2);}

And if you want to use it, you can write this:

int one, two;
std::tie(one, two) = f();

The problem with this approach is that you need to define 'one' and 'two' and then assign them to the return value of f(). It would be better if we can write something like

auto {one, two} = f();

I watched a lecture (I don't remember which one, sorry) in which the speaker said that the C++ standard people where trying to do something like that. I think this lecture is from 2 years ago. Does anyone know if right now (in almost c++17) you can do it or something similar?

Also available in [Microsoft Visual Studio Community 2017 Preview (2)](https://www.visualstudio.com/vs/preview/). — wally, Aug 31 '17 at 14:55

score 14 · Answer 1 · edited Sep 01 '17 at 09:50

14

Yes, there is something called structured bindings that allows for multiple values to be initialized in that way.

The syntax uses square brackets however:

#include <utility>

std::pair<int, int> f()
{
    //return std::make_pair(1, 2); // also works, but more verbose
    return { 1, 2 };
}

int main()
{
    auto[one, two] = f();
}

demo

edited Sep 01 '17 at 09:50

MSalters

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answered Aug 31 '17 at 14:43

wally

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Two nitpicks: 1. `#include ` instead of ``. 2. You can now `return {1, 2};`. – Howard Hinnant Aug 31 '17 at 15:02
@HowardHinnant Good point about the return. I was trying to keep the question's code as similar as possible to highlight the key differences. Interesting note about `` vs `` inclusion. Why is `#include ` preferred? (PS. thanks for an awesome time library) – wally Aug 31 '17 at 15:07
Thanks! :-) `pair` has lived in `` since C++98, and the "new `tie`" doesn't require ``. – Howard Hinnant Aug 31 '17 at 15:09
Nice! +1 ... :-) – Howard Hinnant Aug 31 '17 at 15:12

Next generation of std::tie

1 Answers1