[zozbot234]

.await is a postfix keyword - it effectively means "crazy control-flow (monadic) magic is happening here". "?" for failure handling is another bit of postfix syntax, that means something very similar. A good IDE will show it with a different highlight, so that it will never be confused for a struct member or method call.

This stuff was discussed by the community for a long time - bikeshedding about syntax is a well-known "trap" in programming language design. It has turned out to be (IMHO) reasonably intuitive, and preferable to the alternatives.

[CJefferson]

My biggest problem with await is it's very non-obvious if you don't know to expect.

Seeing a '?' is obviously a "new thing", so people go look up what it is (in practice, I would expect any Rust programmer to learn '?' really early, but if they somehow miss learning it, they will know to go look it up).

I've seen beginners assume they were "missing the await member". Of course, once you know it's something new you can learn it. I would have prefered something like .!await, just to make clear it's a "new thing".

[dgellow]

Isn't "?" just a sugar for something like the following? That's how I think about it in my mind at least.

  // with "?"
  let v = x?;

  // without "?"
  let v = match x {
    Ok(o) => Ok(o),
    Err(e) => return Err(e), // exit current scope due to the return
  }.unwrap();

That feels like something that could be done with a macro.

[estebank]

It's more like

  let v = match x {
    Ok(o) => o,
    Err(e) => return Err(e.into()),
  };

> That feels like something that could be done with a macro.

Indeed. It used to be a macro called try!.

[dgellow]

Ah, thanks for the correction, that's better yes

[zozbot234]

Yes, that's control flow magic. It was prototyped with a macro, but failure handling comes up all the time in practical programming, and it's important to make it as ergonomic as possible.

[dgellow]

I see. I think reading your initial comment I took issue with the hyperbole "crazy control-flow (monadic) magic is happening here".

But yes it is a hidden control flow, and taking in account hidden control flows is inherently more complicated (or at least has a steeper learning curve).