[insanitybit]

The short answer is... yeah, just clone the objects. Whatever other languages are doing is going to have the same tradeoff - performance (or safety, if the other languages aren't memory safe). Iff it becomes a problem, come back later and remove the '.clone()'.

[zozbot234]

You can also use Cow<> to choose between cloning and and immutable borrowing at runtime.

[insanitybit]

Unless you're using `'static` you will still run into lifetimes with Cow, which I suspect a lot of people will find difficult. I'd suggest just using clone, learning the broader language, and learning about lifetime stuff later.

Lifetimes aren't hard or complicated, what's complicated is understand their interaction with other features (closures) when you don't even understand wtf closures in rust are, or traits, etc. I'd just focus on the other stuff for as long as you can.

[aussiesnack]

> Lifetimes aren't hard or complicated,

Untrue - read https://users.rust-lang.org/t/what-is-a-good-mental-model-of.... Even Rust aficionados can't describe how they work without vast screeds. Or if you think the posters there are just wrong, try the RFC on which the current implementation is based: https://rust-lang.github.io/rfcs/2094-nll.html. You truly don't find that hard or complicated?

It may be the case that people can use simplified subsets of the language to ease their way. But when a Rust advocate says that in effect to understand lifetimes you have to read the standard library source (as is written in the forum thread linked above), because no current documentation is comprehensive enough to cover it, then you know the whole thing itself is pretty complex.

[insanitybit]

> You truly don't find that hard or complicated?

This is like saying: "You think a 64bit integer is simple? OK, let's dig into the C memory model, twos complement, overflow CPU flags, how CPU caches are implemented, architectural nuances that can lead to unsynced writes from registers to RAM, etc". In reality most people can just learn that it's a number that holds 2^64 values, not complicated. If you want to really understand integers though go read the intel manual and the C memory model specification.

Are lifetimes complicated? If you're a compiler developer who needs to consider the implications across all features and edge cases, yes. If you're learning the language and you just want to write "find me a &str in another &str but don't clone it", no, it's not complicated at all.

The vast majority of beginners can just learn "& means any number of readers and no writers, &mut means one writer and no readers".

[aussiesnack]

> The vast majority of beginners can just learn "& means any number of readers and no writers, &mut means one writer and no readers".

But 'beginning' is never the hard part of learning any programming language, at least for a programmer. The hard part is going from having learned the basics to getting stuff done. Rust is harder than any other mainstream language to do that in. The writers in that thread can't even describe their mental model (NOT the underlying tech as you claim) of lifetimes without vast elliptical descriptions. And they can't point to any straightforward documentation.

I have learned multiple programming languages, of many different paradigms, and never had the trouble getting to the stage of writing useful software that I have had with Rust. I've witnessed the same again and again with all the people I know - all professional programmers. In fact I'm the only one I know who's stayed with it.

I find the denial of Rust's difficulty (and not even centred on the borrow checker - it's the use of just about every commmon library) just very very strange. Odd enough (and distant enough from the obvious, adn the experience of every person I've known) that I find it completely incomprehensible.

[nicoburns]

> Rust is harder than any other mainstream language to do that in.

I’d argue C and C++ are both harder. It’s hard to even get these to build once you move past trivia examples (including libraries etc).

> I find the denial of Rust's difficulty (and not even centred on the borrow checker - it's the use of just about every commmon library) just very very strange

Some of us just didn’t find it that hard. Like, I get that its hard for people in theory, because I’ve seen enough people express this that I believe it must be a common experience. But my personal experience was a couple of weeks of slow progress and lots of puzzling, and then everything became much easier, coupled with a joy that most of the language is so much better designed than the previous generation of languages I was used to using (e.g. it actually has sum types, and everything is an expression - why on earth doesn’t every language work like this)

[insanitybit]

The rust borrow checker has been described in trivial terms many times. The first time I had it explained, as I recall, was as a book.

You own a book.

`&` - You can lend others the book, they can't fuck with it. `&mut` - You can lend the book to one person, they can fuck with it `move` - You give someone else the book, it's theirs now

Or `many reader NAND one writer`

Is this a complete explanation? No. But it's quite simple and you can be plenty productive with just this amount of understanding.

Your experience is not my experience. I used Rust for the first project I wrote as an intern after dropping out, having never used it before, and I even used it to interact with mysql, which I had never used before.

At my last company I had multiple people pick up rust in a matter of days.

I'm not denying rust as being difficult, I'm saying it's easy for some and hard for some. I found it easy, I was writing productive code on day 0 with virtually no preparation other than that I wanted to try it out. Many people find it easy. Obviously some people, many people, find it hard. Life's weird like that.

[jcranmer]

From the standpoint of being productive in Rust, this is what you need to know:

* An object has a lifetime. This generally lasts until overwritten or destroyed at end of scope.

* You can loan out references to this object. You can either have a single &mut, xor an unlimited number of & references, but not both.

* References cannot outlast the lifetime of the object they point to.

* If you have a &mut reference to an object, you can give out another &mut reference to the same object. But you can't use the first reference for the duration of the second.

* Lifetimes can be named, and you can express criteria of the form "this lifetime must at least/most this long."

* Bonus: if you have &mut x, you can give out &mut x.a and &mut x.b at the same time. But you can't give out &mut x while such a subreference is live.

And... that's really all you need. Yeah, there's a lot more rules, and there's definitely fun edge cases around things like temporary objects' lifetimes. But there's no need to know all of that stuff. If you get things wrong, the compiler will come back and slap you in the face and give you an error message--that's the selling point of Rust, getting lifetimes wrong is an error, not silent nonsense--and your task at that point is to figure out if you're really breaking a cardinal rule (two or more mutable references to the same memory location, or references not lasting long enough), or if you didn't enforce sufficiently strict requirements for the bounds of the lifetimes. And the rust compiler is pretty good at telling you what you have to do to get necessary lifetime bounds (sometimes too good--it can suggest fixes to lifetime bounds even when such bounds are unachievable).

I'd compare this to things like name lookup and overload resolution in C++, which are actually horrendously confusing algorithms that almost nobody understands in their entirety. Yet plenty of people can be productive in C++ because the general principles are well-understood, and if you're at the point where you need to descend into the morass of exceptions and exceptions-to-exceptions, you're probably writing confusing code to begin with.

[zozbot234]

> Rust is harder than any other mainstream language to do that in.

It's not hard, you just add boilerplate. Cloning data, using interior mutability, or adding ref counting to deal with cases where multiple "owners" can keep an object around independently.

Then removing the boilerplate is how you do optimization, once you've gotten things to work. The opposite of other languages where low-level code is the most verbose and least intuitive.

[TylerE]

Ok, so how do I do one writer and one or more readers?