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Comment by zelos | Hacker News Reader

There are some nice things in there, but the destructuring looks a bit odd:

  struct S { int x1 : 2; volatile double y1; };
  S f();
  const auto [ x, y ] = f();

So it's just ordering based, I can't pull out one member by name?

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C++ already had syntax for pulling out one member by name: ;)

    const auto x = f().x1;

I'm not sure what the wink means, but I think gp might be talking about destructuring like what you'd find in Javascript:

  > const {a, b} = {a: 'hey', b: 'there'}
  undefined
  > a
  'hey'
  > b
  'there'

It's yet another feature stolen from Python.

Next version maybe they will even allow stuff like

  [x, [y, z]] = f()

  [x, y, z...] = f()

These ideas are a lot older than python, about as old as multiple return values.

C++ has tuple<> for this.

it has to work with unnamed tuples:

const auto [ x, y ] = make_tuple(1, 23);

Tuples are ordered though. I don't usually think of structs by the order the properties are declared - I usually think of them by name.

I am, admittedly, not primarily a c++ dev though. Are structs typically ordered data structures in c++?

There is no struct here.

x will be an independent variable which will take the first value from the tuple, and y the second one.

His point is that it makes sense to destructure in order for tuples, but what makes sense for structs is destructuring by field name.

> Tuples are ordered though. I don't usually think of structs by the order the properties are declared - I usually think of them by name.

Think for instance of a 2D point structure. There are tons of implementations, all with different naming conventions ; or sometimes storing them in an array. This allows to just do :

    auto [x, y] = someRandomLibraryPoint();

> I don't usually think of structs by the order the properties are declared

In C++ you have to, since it's guaranteed by the language that members are initialized in order of declaration (within the struct). And, like C of course, it also determines memory layout, padding and alignment

> Are structs typically ordered data structures in c++

Yes, and compilers like Clang even let you inspect their memory layout

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