My experience rewriting Enjarify in Rust

Re:My experience rewriting Enjarify in Rust by unethical_ban on Monday September 19, 2016 @02:41PM (#12533656)

Hi Steve, I've been working on learning Rust from a beginner perspective (know some Python, never written a program with more than 500 loc). However, I do know what pointers are, and get the concept of stack and heap.

My comment is this: It is not immediately apparent that when using &var syntax, Rust is "auto-dereferencing" the variable to get the value. It took a moment to wrap my head around why

  println!("{}", &x); //this can show "5".

Rust's ownership/borrowing mechanism, where variables basically "die" if you don't pass by reference, is confusing until I read the FAQ and those three chapters in the Book a few times.

What I think the Book, or some other reference, needs is a "best practices for newbies" guide. Kind of like how we learn the atom is the smallest possible object in high school, I think it would be ok for a doc like this to tell newbies "You almost never want to pass a variable by value". It would help keep people from fighting the borrow checker.

Let me know if I'm crazy.

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Re:My experience rewriting Enjarify in Rust by steveklabnik on Monday September 19, 2016 @02:57PM (#12533801)

Hey hey! So, this specific example has nothing to do with auto dereferencing in the language. It's that Display, implemented for &T, displays the value instead of the reference. This is what you want 99% of the time, so Rust is trying to Do The Right Thing here. If you want to print out the numeric version of the pointer, {:p} will do it. It's a bit tough to document specific implementations at the moment, so it's certainly not as clear as it could be. you're right.

( For reference, this implementation is here: https://github.com/rust-lang/rust/blob/master/src/libcore/fm... note that this is in a macro to do this for all of the traits at once...)

I'm actually re-writing the book right now, and one of the things I'm focusing hard on is the stuff around ownership and borrowing. The current chapters are too abstract, the new ones are focused on String/&str. You can find that here: http://rust-lang.github.io/book/ch04-00-understanding-owners...

  > "You almost never want to pass a variable by value".

So, the issue with advice like this is that it's not always true: you almost never want to pass some things by value, but Copy types, for example, you almost always want to pass by value. It's tricky!

That said, it's true that learning Rust can be tricky; we're trying to focus on improving that in the coming year. So keep it coming! This kind of feedback is very helpful, thank you.

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