[spacechild1]

> Yes, you could make the same mistake without auto, but it's easier to notice.

Is it really? I rather think that a missing & is easier to spot with "auto" simply because there is less text to parse for the eye.

> If you see "for (auto v : vec)" looks good right?

For me the missing & sticks out like a sore thumb.

> It's easy to forget (or not notice) that auto will not resolve to a reference in this case

Every feature can be misused if the user forgets how it works. I don't think people suddenly forget how "auto" works, given how ubiquitous it is.

[tialaramex]

It's a foot gun. Why is the default target for this gun my foot? "You should be careful to choose the target properly" isn't an answer to that question.

[gpderetta]

In what way it is a footgun? auto x = ... ; does what I would expect. Copying is usually the default in C++ and that's what I would expect to happen here.

If auto deduced reference types transparently, it would actually be more dangerous.

[tialaramex]

Copying is a weird default because who said that's even achievable, let alone cheap?

So I guess I depart from you there and thus my issue here is not really about auto

[spacechild1]

C++ has value semantics, which means that values of user-defined types generally behave like values of built-in types. In this sense, copying is the only logical default. It's just how the language has been designed.

Things are different in Rust because of lifetimes and destructive moves. In this context, copying would be a bad default indeed.

> because who said that's even achievable, let alone cheap?

Nobody said that. The thing is that user-defined types can be anything from tiny and cheap to huge and expensive. A language has to pick one default and be consistent. You can complain one way or the other.

[1718627440]

I find passing by value to be sensible, but the allocating part sounds like a bad idea. Passing the value of something doesn't imply making a copy, if the value is never changed, it can be entirely optimized away.

[spacechild1]

> Passing the value of something doesn't imply making a copy

Yes, languages like Rust can automatically move variables if the compiler can prove that they will not be used anymore. Unfortunately, this is not possible in C++, so the user has to move explicitly (with std::move).

[spacechild1]

That's exactly what I was about to write!